feat(ui): do not sample alpha in Canvas color picker

Closes #7897

Author: psychedelicious

invokeai/frontend/web/src/features/controlLayers/konva/CanvasStateApiModule.ts

@@ -231,7 +231,7 @@ export class CanvasStateApiModule extends CanvasModuleBase {
   /**
    * Sets the drawing color, pushing state to redux.
    */
-  setColor = (color: RgbaColor) => {
+  setColor = (color: Partial<RgbaColor>) => {
     return this.store.dispatch(settingsColorChanged(color));
   };
 

invokeai/frontend/web/src/features/controlLayers/konva/CanvasTool/CanvasColorPickerToolModule.ts

@@ -406,8 +406,8 @@ export class CanvasColorPickerToolModule extends CanvasModuleBase {
   };
 
   onStagePointerUp = (_e: KonvaEventObject<PointerEvent>) => {
-    const color = this.$colorUnderCursor.get();
-    this.manager.stateApi.setColor({ ...color, a: color.a / 255 });
+    const { a: _, ...color } = this.$colorUnderCursor.get();
+    this.manager.stateApi.setColor(color);
   };
 
   onStagePointerMove = (_e: KonvaEventObject<PointerEvent>) => {

invokeai/frontend/web/src/features/controlLayers/store/canvasSettingsSlice.ts

@@ -134,8 +134,8 @@ const slice = createSlice({
     settingsEraserWidthChanged: (state, action: PayloadAction<CanvasSettingsState['eraserWidth']>) => {
       state.eraserWidth = Math.round(action.payload);
     },
-    settingsColorChanged: (state, action: PayloadAction<CanvasSettingsState['color']>) => {
-      state.color = action.payload;
+    settingsColorChanged: (state, action: PayloadAction<Partial<CanvasSettingsState['color']>>) => {
+      state.color = { ...state.color, ...action.payload };
     },
     settingsInvertScrollForToolWidthChanged: (
       state,