Fix allowTransparency in lib and demo

Fixes #5558
Fixes #5560

src/common/Color.test.ts

@@ -303,6 +303,9 @@ describe('Color', () => {
         assert.deepEqual(css.toColor('rgba(0, 0, 80, 0.5)'), { css: '#00005080', rgba: 0x00005080 });
         assert.deepEqual(css.toColor('rgba(255, 255, 255, 1)'), { css: '#ffffffff', rgba: 0xffffffff });
       });
+      it('should convert "transparent" to an IColor', () => {
+        assert.deepEqual(css.toColor('transparent'), { css: 'transparent', rgba: 0x00000000 });
+      });
     });
   });
 

src/common/Color.ts

@@ -184,6 +184,14 @@ export namespace css {
       return channels.toColor($r, $g, $b, $a);
     }
 
+    // Handle the "transparent" keyword
+    if (css === 'transparent') {
+      return {
+        css: 'transparent',
+        rgba: 0x00000000
+      };
+    }
+
     // Validate the context is available for canvas-based color parsing
     if (!$ctx || !$litmusColor) {
       throw new Error('css.toColor: Unsupported css format');