Introduce is256Color helper

src/renderer/TextRenderLayer.ts

@@ -9,6 +9,7 @@ import { CharData, ITerminal } from '../Types';
 import { INVERTED_DEFAULT_COLOR, DEFAULT_COLOR } from './atlas/Types';
 import { GridCache } from './GridCache';
 import { BaseRenderLayer } from './BaseRenderLayer';
+import { is256Color } from './atlas/CharAtlasUtils';
 
 /**
  * This CharData looks like a null character, which will forc a clear and render
@@ -186,7 +187,7 @@ export class TextRenderLayer extends BaseRenderLayer {
       let nextFillStyle = null; // null represents default background color
       if (bg === INVERTED_DEFAULT_COLOR) {
         nextFillStyle = this._colors.foreground.css;
-      } else if (bg < DEFAULT_COLOR) {
+      } else if (is256Color(bg)) {
         nextFillStyle = this._colors.ansi[bg].css;
       }
 
@@ -230,7 +231,7 @@ export class TextRenderLayer extends BaseRenderLayer {
         this._ctx.save();
         if (fg === INVERTED_DEFAULT_COLOR) {
           this._ctx.fillStyle = this._colors.background.css;
-        } else if (fg < DEFAULT_COLOR) {
+        } else if (is256Color(fg)) {
           // 256 color support
           this._ctx.fillStyle = this._colors.ansi[fg].css;
         } else {