Add nuke fallout color graphics option (#4355)

## What

Adds a **Nuke fallout color** option to the in-game graphics settings
modal (Effects section), letting players recolor the fallout tint left
on territory after a nuke.

![modal](https://github.com/user-attachments/assets/placeholder)

## How

Mirrors the existing **Ocean color** override pattern:

- `GraphicsOverrides.ts` — adds `staleNukeColor` (hex string) to the
`mapOverlay` override schema.
- `RenderOverrides.ts` — `applyGraphicsOverrides` parses the hex and
writes the renderer's `staleNukeR/G/B` 0–1 float channels (`hexToRgb`
yields 0–255, so it divides by 255).
- `GraphicsSettingsModal.ts` — new hex-text + native color-picker row,
default computed from `render-settings.json`.
- `en.json` — `nuke_color_label` / `nuke_color_desc`.

The value persists via `UserSettings.graphicsOverrides()` and is cleared
by the modal's existing "Reset to defaults".

The render debug GUI already exposes the same setting as **Stale Nuke
Color** (Map Overlay), so no change was needed there.

## Testing

- `tsc --noEmit` clean.
- Verified in a headless solo game: the row renders with the green
default (`#0d8c12`), changing it persists `mapOverlay.staleNukeColor`,
and `applyGraphicsOverrides("#ff0000")` produces `staleNukeR=1, G=0,
B=0`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

resources/lang/en.json

@@ -547,6 +547,8 @@
     "name_cull_desc": "Hide names smaller than this size",
     "name_cull_label": "Minimum name size",
     "name_scale_label": "Name Scale",
+    "nuke_color_desc": "Color of the fallout tint left on territory after a nuke.",
+    "nuke_color_label": "Nuke fallout color",
     "ocean_color_desc": "Base color of ocean.",
     "ocean_color_label": "Ocean color",
     "rail_distance_desc": "How far zoomed out train tracks remain visible",

src/client/hud/layers/GraphicsSettingsModal.ts

@@ -115,6 +115,22 @@ function falloffToUnitGlowSlider(falloff: number): number {
 
 const HEX_COLOR_RE = /^#?([0-9a-fA-F]{6})$/;
 
+// The stale-nuke (fallout ground tint) color is stored in render-settings.json
+// as three 0-1 floats; the color picker wants a "#rrggbb" hex string.
+function rgbFloatsToHex(r: number, g: number, b: number): string {
+  const ch = (v: number) =>
+    Math.round(v * 255)
+      .toString(16)
+      .padStart(2, "0");
+  return `#${ch(r)}${ch(g)}${ch(b)}`;
+}
+
+const NUKE_COLOR_DEFAULT = rgbFloatsToHex(
+  renderDefaults.mapOverlay.staleNukeR,
+  renderDefaults.mapOverlay.staleNukeG,
+  renderDefaults.mapOverlay.staleNukeB,
+);
+
 export class ShowGraphicsSettingsModalEvent {
   constructor(
     public readonly isVisible: boolean = true,
@@ -356,6 +372,20 @@ export class GraphicsSettingsModal extends LitElement implements Controller {
     this.patchMapOverlay({ coordinateGridOpacity: value });
   }
 
+  private currentNukeColor(): string {
+    return (
+      this.userSettings.graphicsOverrides().mapOverlay?.staleNukeColor ??
+      NUKE_COLOR_DEFAULT
+    );
+  }
+
+  private onNukeColorChange(event: Event) {
+    const value = (event.target as HTMLInputElement).value.trim();
+    const match = HEX_COLOR_RE.exec(value);
+    if (!match) return; // ignore partial/invalid hex while typing
+    this.patchMapOverlay({ staleNukeColor: `#${match[1].toLowerCase()}` });
+  }
+
   private onRailDrawDistanceChange(event: Event) {
     const drawDistance = parseFloat((event.target as HTMLInputElement).value);
     // Invert: higher draw distance => tracks visible when more zoomed out.
@@ -572,6 +602,7 @@ export class GraphicsSettingsModal extends LitElement implements Controller {
     const railDrawDistance = RAIL_ZOOM_MAX - this.currentRailMinZoom();
     const railThickness = this.currentRailThickness();
     const oceanColor = this.currentOceanColor();
+    const nukeColor = this.currentNukeColor();
     const ambientLevel = this.currentAmbientLevel();
     const unitGlow = this.currentUnitGlow();
     const colorblind = this.currentColorblind();
@@ -1123,6 +1154,33 @@ export class GraphicsSettingsModal extends LitElement implements Controller {
               />
             </div>
 
+            <div
+              class="flex gap-3 items-center w-full text-left p-3 hover:bg-slate-700 rounded-sm text-white transition-colors"
+            >
+              <div class="flex-1">
+                <div class="font-medium">
+                  ${translateText("graphics_setting.nuke_color_label")}
+                </div>
+                <div class="text-sm text-slate-400">
+                  ${translateText("graphics_setting.nuke_color_desc")}
+                </div>
+              </div>
+              <input
+                type="text"
+                .value=${nukeColor}
+                placeholder=${NUKE_COLOR_DEFAULT}
+                spellcheck="false"
+                @change=${this.onNukeColorChange}
+                class="w-24 px-2 py-1 bg-slate-900 border border-slate-500 rounded-sm text-sm text-white font-mono"
+              />
+              <input
+                type="color"
+                .value=${nukeColor}
+                @input=${this.onNukeColorChange}
+                class="w-10 h-8 bg-transparent border border-slate-500 rounded-sm cursor-pointer"
+              />
+            </div>
+
             <div
               class="px-3 py-1 text-xs font-semibold text-slate-400 uppercase tracking-wider mt-2"
             >

src/client/render/gl/GraphicsOverrides.ts

@@ -27,6 +27,9 @@ export const GraphicsOverridesSchema = z
         territorySaturation: z.number(),
         territoryAlpha: z.number(),
         coordinateGridOpacity: z.number(),
+        // "#rrggbb" hex string; overrides the lingering fallout ground tint
+        // left on territory after a nuke.
+        staleNukeColor: z.string(),
       })
       .partial(),
     railroad: z

src/client/render/gl/RenderOverrides.ts

@@ -1,5 +1,6 @@
 import type { GraphicsOverrides } from "./GraphicsOverrides";
 import { createThemeSettings, type RenderSettings } from "./RenderSettings";
+import { hexToRgb } from "./utils/ColorUtils";
 
 /**
  * Apply the user's graphics overrides onto a RenderSettings in place: name
@@ -64,6 +65,15 @@ export function applyGraphicsOverrides(
     settings.mapOverlay.coordinateGridOpacity =
       overrides.mapOverlay.coordinateGridOpacity;
   }
+  if (overrides.mapOverlay?.staleNukeColor !== undefined) {
+    // hexToRgb yields 0-255 channels; the stale-nuke uniforms are 0-1 floats.
+    const rgb = hexToRgb(overrides.mapOverlay.staleNukeColor);
+    if (rgb !== null) {
+      settings.mapOverlay.staleNukeR = rgb[0] / 255;
+      settings.mapOverlay.staleNukeG = rgb[1] / 255;
+      settings.mapOverlay.staleNukeB = rgb[2] / 255;
+    }
+  }
   if (overrides.railroad?.railMinZoom !== undefined) {
     settings.railroad.railMinZoom = overrides.railroad.railMinZoom;
   }