diff --git a/src/client/EffectsInput.ts b/src/client/EffectsInput.ts
index 3285c562f..f9404b73b 100644
--- a/src/client/EffectsInput.ts
+++ b/src/client/EffectsInput.ts
@@ -8,7 +8,7 @@ import {
   EFFECTS_KEY,
   USER_SETTINGS_CHANGED_EVENT,
 } from "../core/game/UserSettings";
-import { renderTransportShipTrailSwatch } from "./components/EffectPreview";
+import "./components/EffectPreview"; // registers <trail-swatch>
 import { fetchCosmetics, getPlayerCosmetics } from "./Cosmetics";
 import { crazyGamesSDK } from "./CrazyGamesSDK";
 import { translateText } from "./Utils";
@@ -87,9 +87,12 @@ export class EffectsInput extends LitElement {
           >
             ${translateText("effects.title")}
           </span>`
-        : html`<span class="w-full h-full p-1.5"
-            >${renderTransportShipTrailSwatch(this.trailAttributes)}</span
-          >`;
+        : html`<span class="w-full h-full p-1.5">
+            <trail-swatch
+              class="block w-full h-full"
+              .trail=${this.trailAttributes}
+            ></trail-swatch>
+          </span>`;
 
     return html`
       <button
diff --git a/src/client/WebGLFrameBuilder.ts b/src/client/WebGLFrameBuilder.ts
index 84ae010a0..bf2ecd204 100644
--- a/src/client/WebGLFrameBuilder.ts
+++ b/src/client/WebGLFrameBuilder.ts
@@ -308,11 +308,13 @@ export class WebGLFrameBuilder {
   }
 
   /**
-   * Encode a player's transport-ship-trail gradient into the effect palette.
+   * Encode a player's transport-ship-trail effect into the effect palette.
    * Layout matches trail.frag.glsl: row r holds color r's rgb, and the spare
-   * alpha channels carry the gradient's scalar params — row 0's alpha = color
-   * count (0 → the shader falls back to the territory color), row 1's alpha =
-   * colorSize (band width), row 2's alpha = movementSpeed (scroll rate).
+   * alpha channels (rows 0–3 always exist) carry the scalar params —
+   *   row 0.a = color count (0 → the shader falls back to the territory color),
+   *   row 1.a = styleId (0 = gradient, 1 = transition),
+   *   row 2.a = scalar0 (gradient: colorSize; transition: frequency),
+   *   row 3.a = scalar1 (gradient: movementSpeed; transition: unused).
    * colord doesn't throw on a bad color string (it returns black), so unparseable
    * colors are dropped — leaving an empty list, which falls back to the territory
    * color rather than rendering black. Returns whether any color was written.
@@ -334,11 +336,14 @@ export class WebGLFrameBuilder {
       this.effectPalette[off + 2] = c.b / 255;
       this.effectPalette[off + 3] = 0;
     }
-    // Scalar params packed into spare alpha channels (rows 0–2 always exist).
+    const [styleId, scalar0, scalar1] =
+      attrs.type === "transition"
+        ? [1, attrs.frequency, 0]
+        : [0, attrs.colorSize, attrs.movementSpeed];
     this.effectPalette[(0 * PALETTE_SIZE + smallID) * 4 + 3] = colors.length;
-    this.effectPalette[(1 * PALETTE_SIZE + smallID) * 4 + 3] = attrs.colorSize;
-    this.effectPalette[(2 * PALETTE_SIZE + smallID) * 4 + 3] =
-      attrs.movementSpeed;
+    this.effectPalette[(1 * PALETTE_SIZE + smallID) * 4 + 3] = styleId;
+    this.effectPalette[(2 * PALETTE_SIZE + smallID) * 4 + 3] = scalar0;
+    this.effectPalette[(3 * PALETTE_SIZE + smallID) * 4 + 3] = scalar1;
     return colors.length > 0;
   }
 
diff --git a/src/client/components/CosmeticButton.ts b/src/client/components/CosmeticButton.ts
index ec1ba3f6d..ef17fa7da 100644
--- a/src/client/components/CosmeticButton.ts
+++ b/src/client/components/CosmeticButton.ts
@@ -19,7 +19,7 @@ import { translateText } from "../Utils";
 import "./CapIcon";
 import "./CosmeticContainer";
 import "./CosmeticInfo";
-import { renderTransportShipTrailSwatch } from "./EffectPreview";
+import "./EffectPreview"; // registers <trail-swatch>
 import { renderPatternPreview } from "./PatternPreview";
 import "./PlutoniumIcon";
 
@@ -187,7 +187,10 @@ export class CosmeticButton extends LitElement {
         </div>`;
       }
       // Only effectType today is transportShipTrail; c.attributes is its style.
-      return renderTransportShipTrailSwatch(c.attributes);
+      return html`<trail-swatch
+        class="block w-full h-full"
+        .trail=${c.attributes}
+      ></trail-swatch>`;
     }
 
     if (this.activeResolved.type === "pack") {
diff --git a/src/client/components/EffectPreview.ts b/src/client/components/EffectPreview.ts
index afee3dcf6..c58fb4e02 100644
--- a/src/client/components/EffectPreview.ts
+++ b/src/client/components/EffectPreview.ts
@@ -1,27 +1,78 @@
-import { html, TemplateResult } from "lit";
+import { html, LitElement, TemplateResult } from "lit";
+import { customElement, property } from "lit/decorators.js";
 import { TransportShipTrailAttributes } from "../../core/CosmeticSchemas";
 
 // Neutral fallback when a trail has no usable colors.
 const EMPTY_BG = "#444";
 
 /**
- * Render a swatch preview of a transport-ship-trail's attributes, filling its
- * container. A trail is a list of colors: one color renders as a flat swatch,
- * two or more as a left-to-right gradient (a multi-color list reads as a
- * rainbow). An empty list renders a neutral swatch.
+ * Swatch preview of a transport-ship-trail effect, filling its container.
+ *
+ * - gradient / single color: a static swatch (flat color or left-to-right
+ *   gradient — a multi-color list reads as a rainbow).
+ * - transition: cross-fades through the colors over time, mirroring the trail
+ *   (each color step lasts 1/frequency seconds, matching the shader).
  */
-export function renderTransportShipTrailSwatch(
-  attributes: TransportShipTrailAttributes,
-): TemplateResult {
-  const colors = attributes.colors;
-  const background =
-    colors.length === 0
-      ? EMPTY_BG
-      : colors.length === 1
-        ? colors[0]
-        : `linear-gradient(90deg,${colors.join(",")})`;
-  return html`<div
-    class="w-full h-full rounded-md"
-    style="background:${background};"
-  ></div>`;
+@customElement("trail-swatch")
+export class TrailSwatch extends LitElement {
+  // Named `trail` (not `attributes`) to avoid clashing with Element.attributes.
+  @property({ attribute: false })
+  trail: TransportShipTrailAttributes | null = null;
+
+  private animation: Animation | null = null;
+
+  // Light DOM so the shared Tailwind classes apply.
+  createRenderRoot(): HTMLElement {
+    return this;
+  }
+
+  render(): TemplateResult {
+    const colors = this.trail?.colors ?? [];
+    let background: string;
+    if (colors.length === 0) {
+      background = EMPTY_BG;
+    } else if (this.trail?.type === "transition") {
+      // The animation (see updated) cross-fades from here through the list.
+      background = colors[0];
+    } else if (colors.length === 1) {
+      background = colors[0];
+    } else {
+      background = `linear-gradient(90deg,${colors.join(",")})`;
+    }
+    return html`<div
+      class="w-full h-full rounded-md"
+      style="background:${background};"
+    ></div>`;
+  }
+
+  updated(changed: Map<string, unknown>): void {
+    if (!changed.has("trail")) return;
+    this.animation?.cancel();
+    this.animation = null;
+
+    const attrs = this.trail;
+    if (attrs?.type !== "transition") return;
+    const colors = attrs.colors;
+    if (colors.length < 2 || attrs.frequency <= 0) return;
+
+    const fill = this.querySelector<HTMLElement>("div");
+    if (!fill) return;
+
+    // Cross-fade color0 → color1 → … → color0; each step lasts 1/frequency s,
+    // matching the shader's i = floor(uTime * frequency) mod count.
+    const keyframes = [...colors, colors[0]].map((c) => ({
+      backgroundColor: c,
+    }));
+    this.animation = fill.animate(keyframes, {
+      duration: (colors.length / attrs.frequency) * 1000,
+      iterations: Infinity,
+      easing: "linear",
+    });
+  }
+
+  disconnectedCallback(): void {
+    super.disconnectedCallback();
+    this.animation?.cancel();
+    this.animation = null;
+  }
 }
diff --git a/src/client/render/gl/shaders/map-overlay/trail.frag.glsl b/src/client/render/gl/shaders/map-overlay/trail.frag.glsl
index 8ab748451..cc2144d5c 100644
--- a/src/client/render/gl/shaders/map-overlay/trail.frag.glsl
+++ b/src/client/render/gl/shaders/map-overlay/trail.frag.glsl
@@ -5,13 +5,15 @@ precision highp usampler2D;
 uniform usampler2D uTrailTex;     // R8UI — trail ownerID per cell (0 = none)
 uniform sampler2D  uPalette;      // RGBA32F — player colors
 uniform sampler2D  uAffiliation;  // RGBA8 — affiliation colors (row 0 = border, row 1 = unit)
-uniform sampler2D  uEffect;       // RGBA32F — trail gradient, keyed by ownerID:
+uniform sampler2D  uEffect;       // RGBA32F — trail effect, keyed by ownerID:
                                   //   row r = color r's rgb; spare alphas hold scalars:
                                   //   row 0.a = color count (0 = no effect → territory color),
-                                  //   row 1.a = colorSize (band width), row 2.a = movementSpeed
+                                  //   row 1.a = styleId (0 = gradient, 1 = transition),
+                                  //   row 2.a = scalar0 (gradient colorSize / transition freq),
+                                  //   row 3.a = scalar1 (gradient movementSpeed)
 uniform vec2 uMapSize;
 uniform float uTrailAlpha;
-uniform float uTime;              // seconds, for the flowing gradient animation
+uniform float uTime;              // seconds, for animated effect styles
 uniform int uAltView;
 
 in vec2 vWorldPos;
@@ -40,13 +42,23 @@ void main() {
     } else if (count == 1) {
       // Single color — flat trail.
       color = texelFetch(uEffect, ivec2(owner, 0), 0).rgb;
+    } else if (int(texelFetch(uEffect, ivec2(owner, 1), 0).a + 0.5) == 1) {
+      // transition — the whole trail is one color at a time, cross-fading
+      // through the list over time. frequency = color changes per second.
+      float frequency = texelFetch(uEffect, ivec2(owner, 2), 0).a;
+      float t = uTime * frequency;
+      int i = int(t) % count;
+      int j = (i + 1) % count;
+      vec3 a = texelFetch(uEffect, ivec2(owner, i), 0).rgb;
+      vec3 b = texelFetch(uEffect, ivec2(owner, j), 0).rgb;
+      color = mix(a, b, fract(t));
     } else {
-      // Multiple colors — cyclic gradient banded across the map (world-space
-      // diagonal), scrolling over time so a moving trail shifts hue along it.
-      // colorSize scales the band width (colorSize = 1 is the default size, ~4
-      // tiles per band); movementSpeed = tiles/sec the bands travel.
-      float colorSize = max(texelFetch(uEffect, ivec2(owner, 1), 0).a, 0.001);
-      float movementSpeed = texelFetch(uEffect, ivec2(owner, 2), 0).a;
+      // gradient — cyclic gradient banded across the map (world-space diagonal),
+      // scrolling over time so a moving trail shifts hue along it. colorSize
+      // scales the band width (colorSize = 1 ≈ 4 tiles per band); movementSpeed
+      // = tiles/sec the bands travel.
+      float colorSize = max(texelFetch(uEffect, ivec2(owner, 2), 0).a, 0.001);
+      float movementSpeed = texelFetch(uEffect, ivec2(owner, 3), 0).a;
       // 4.0 = tiles per band at colorSize 1; tune for default band thickness.
       float cycle = colorSize * 4.0 * float(count);
       float phase =
diff --git a/src/core/CosmeticSchemas.ts b/src/core/CosmeticSchemas.ts
index 84c66779a..781920976 100644
--- a/src/core/CosmeticSchemas.ts
+++ b/src/core/CosmeticSchemas.ts
@@ -102,20 +102,28 @@ export const SkinSchema = CosmeticSchema.extend({
 export const EFFECT_TYPES = ["transportShipTrail"] as const;
 export const EffectTypeSchema = z.enum(EFFECT_TYPES);
 
-// A boat trail is a gradient of one or more colors, cycled along the trail. The
-// old solid/rainbow styles are just color lists now: solid = a single color,
-// rainbow = the spectrum, gradient = two or more. The server only ships this
-// "gradient" shape. Colors are unvalidated strings here; the renderer drops any
-// it can't parse (and an empty list falls back to the player's territory color).
-// `colorSize` is how wide each color band is, in tiles (larger = bigger bands);
-// `movementSpeed` is how fast the bands scroll along the trail, in tiles per
-// second (0 = static).
-export const TransportShipTrailAttributesSchema = z.object({
-  type: z.literal("gradient"),
-  colors: z.array(z.string()),
-  colorSize: z.number(),
-  movementSpeed: z.number(),
-});
+// A boat trail effect, discriminated on `type`:
+//  - "gradient": the colors form a spatial gradient banded along the trail.
+//    `colorSize` = band width in tiles (larger = bigger bands); `movementSpeed`
+//    = how fast the bands scroll, in tiles/sec (0 = static).
+//  - "transition": the whole trail is one color at a time, cross-fading through
+//    the color list over time. `frequency` = color changes per second.
+// solid = a single-color list; rainbow = the spectrum as a gradient. Colors are
+// unvalidated strings here; the renderer drops any it can't parse (and an empty
+// list falls back to the player's territory color).
+export const TransportShipTrailAttributesSchema = z.discriminatedUnion("type", [
+  z.object({
+    type: z.literal("gradient"),
+    colors: z.array(z.string()),
+    colorSize: z.number(),
+    movementSpeed: z.number(),
+  }),
+  z.object({
+    type: z.literal("transition"),
+    colors: z.array(z.string()),
+    frequency: z.number(),
+  }),
+]);
 
 const TransportShipTrailEffectSchema = CosmeticSchema.extend({
   effectType: z.literal("transportShipTrail"),
diff --git a/tests/CosmeticSchemas.test.ts b/tests/CosmeticSchemas.test.ts
index 3caa7481c..1cdb905ae 100644
--- a/tests/CosmeticSchemas.test.ts
+++ b/tests/CosmeticSchemas.test.ts
@@ -51,7 +51,7 @@ describe("Effect cosmetic schemas", () => {
     });
 
     it("requires the gradient type, colors, colorSize, and movementSpeed", () => {
-      // The old solid/rainbow/pulse styles are gone — only gradient remains.
+      // Unrecognized styles (no discriminated-union member) are rejected.
       expect(
         TransportShipTrailAttributesSchema.safeParse({ type: "solid" }).success,
       ).toBe(false);
@@ -66,6 +66,28 @@ describe("Effect cosmetic schemas", () => {
         false,
       );
     });
+
+    it("parses a transition with a color list and frequency", () => {
+      const parsed = TransportShipTrailAttributesSchema.parse({
+        type: "transition",
+        colors: ["#002aff", "#4805ff"],
+        frequency: 1,
+      });
+      expect(parsed).toEqual({
+        type: "transition",
+        colors: ["#002aff", "#4805ff"],
+        frequency: 1,
+      });
+    });
+
+    it("requires frequency for a transition", () => {
+      expect(
+        TransportShipTrailAttributesSchema.safeParse({
+          type: "transition",
+          colors: ["#002aff", "#4805ff"],
+        }).success,
+      ).toBe(false);
+    });
   });
 
   describe("EffectSchema", () => {