Fill in default color value when completing

src/vs/platform/theme/common/colorRegistry.ts

@@ -89,7 +89,7 @@ class ColorRegistry implements IColorRegistry {
 	public registerColor(id: string, defaults: ColorDefaults, description: string): ColorIdentifier {
 		let colorContribution = { id, description, defaults };
 		this.colorsById[id] = colorContribution;
-		this.colorSchema.properties[id] = { type: 'string', description, format: 'color', pattern: colorPattern, patternErrorMessage: colorPatternErrorMessage };
+		this.colorSchema.properties[id] = { type: 'string', description, format: 'color', default: '#ff0000', pattern: colorPattern, patternErrorMessage: colorPatternErrorMessage };
 		this.colorReferenceSchema.enum.push(id);
 		this.colorReferenceSchema.enumDescriptions.push(description);
 		return id;