1. Removed logic to blend selection with background with 0.3 opacity from ColorManager to a function in color namespace.

2. Changed the DomRenderer and CanvasRenderer where the function defined in color namespace is called.

src/browser/Color.ts

@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { IColor } from 'browser/Types';
+import { IColor, IColorSet } from 'browser/Types';
 
 /**
  * Helper functions where the source type is "channels" (individual color channels as numbers).
@@ -47,6 +47,17 @@ export namespace color {
     const rgba = channels.toRgba(r, g, b);
     return { css, rgba };
   }
+  export function blendSelectionWithBgWithOpacity(colors: IColorSet, opacity: number=0.3): void {
+    const [selectionR, selectionG, selectionB, selectionA] = rgba.toChannels(colors.selection.rgba);
+    // The selection color is opaque. It needs to be blended with background color at 0.3 opacity Issue #2737
+    if (selectionA === 0xFF) {
+      const newAlpha: number = Math.round(opacity*255);
+      colors.selection = {
+        css: channels.toCss(selectionR, selectionG, selectionB, newAlpha),
+        rgba: channels.toRgba(selectionR, selectionG, selectionB, newAlpha)
+      };
+    }
+  }
 
   export function ensureContrastRatio(bg: IColor, fg: IColor, ratio: number): IColor | undefined {
     const result = rgba.ensureContrastRatio(bg.rgba, fg.rgba, ratio);

src/browser/ColorManager.ts

@@ -116,16 +116,6 @@ export class ColorManager implements IColorManager {
     this.colors.cursor = this._parseColor(theme.cursor, DEFAULT_CURSOR, true);
     this.colors.cursorAccent = this._parseColor(theme.cursorAccent, DEFAULT_CURSOR_ACCENT, true);
     this.colors.selection = this._parseColor(theme.selection, DEFAULT_SELECTION, true);
-    const [selectionR, selectionG, selectionB, selectionA] = rgba.toChannels(this.colors.selection.rgba);
-    // The selection color is opaque. It needs to be blended with background color at 0.3 opacity Issue #2737
-    if (selectionA === 0xFF) {
-      const opacity = 0.3;
-      const newAlpha = Math.round(opacity*255);
-      this.colors.selection = {
-        css: channels.toCss(selectionR, selectionG, selectionB, newAlpha),
-        rgba: channels.toRgba(selectionR, selectionG, selectionB, newAlpha)
-      };
-    }
     this.colors.selectionOpaque = color.blend(this.colors.background, this.colors.selection);
     this.colors.ansi[0] = this._parseColor(theme.black, DEFAULT_ANSI_COLORS[0]);
     this.colors.ansi[1] = this._parseColor(theme.red, DEFAULT_ANSI_COLORS[1]);

src/browser/renderer/Renderer.ts

@@ -15,6 +15,7 @@ import { ICharSizeService, ICoreBrowserService } from 'browser/services/Services
 import { IBufferService, IOptionsService, ICoreService } from 'common/services/Services';
 import { removeTerminalFromCache } from 'browser/renderer/atlas/CharAtlasCache';
 import { EventEmitter, IEvent } from 'common/EventEmitter';
+import { color } from 'browser/Color';
 
 let nextRendererId = 1;
 
@@ -44,7 +45,7 @@ export class Renderer extends Disposable implements IRenderer {
     super();
     const allowTransparency = this._optionsService.options.allowTransparency;
     this._characterJoinerRegistry = new CharacterJoinerRegistry(this._bufferService);
-
+    color.blendSelectionWithBgWithOpacity(this._colors);
     this._renderLayers = [
       new TextRenderLayer(this._screenElement, 0, this._colors, this._characterJoinerRegistry, allowTransparency, this._id, this._bufferService, _optionsService),
       new SelectionRenderLayer(this._screenElement, 1, this._colors, this._id, this._bufferService, _optionsService),
@@ -87,7 +88,6 @@ export class Renderer extends Disposable implements IRenderer {
 
   public setColors(colors: IColorSet): void {
     this._colors = colors;
-
     // Clear layers and force a full render
     this._renderLayers.forEach(l => {
       l.setColors(this._colors);

src/browser/renderer/dom/DomRenderer.ts

@@ -53,7 +53,7 @@ export class DomRenderer extends Disposable implements IRenderer {
     @IBufferService private readonly _bufferService: IBufferService
   ) {
     super();
-
+    color.blendSelectionWithBgWithOpacity(this._colors);
     this._rowContainer = document.createElement('div');
     this._rowContainer.classList.add(ROW_CONTAINER_CLASS);
     this._rowContainer.style.lineHeight = 'normal';