Color alpha isn't optional

src/vs/workbench/api/node/extHostTypes.ts

@@ -7,7 +7,7 @@
 import * as crypto from 'crypto';
 
 import URI from 'vs/base/common/uri';
-import { Color as CommonColor, HSLA } from 'vs/base/common/color';
+import { Color as BaseColor, HSLA } from 'vs/base/common/color';
 import { illegalArgument } from 'vs/base/common/errors';
 import * as vscode from 'vscode';
 
@@ -1020,23 +1020,20 @@ export class Color {
 	readonly blue: number;
 	readonly alpha: number;
 
-	constructor(red: number, green: number, blue: number, alpha?: number) {
+	constructor(red: number, green: number, blue: number, alpha: number) {
 		this.red = red;
 		this.green = green;
 		this.blue = blue;
 		this.alpha = alpha;
 	}
 
-	static fromHSLA(hue: number, saturation: number, luminosity: number, alpha?: number): Color {
-		if (!alpha) {
-			alpha = 1;
-		}
-		const color = new CommonColor(new HSLA(hue, saturation, luminosity, alpha)).rgba;
+	static fromHSLA(hue: number, saturation: number, luminance: number, alpha: number): Color {
+		const color = new BaseColor(new HSLA(hue, saturation, luminance, alpha)).rgba;
 		return new Color(color.r, color.g, color.b, color.a / 255);
 	}
 
 	static fromHex(hex: string): Color {
-		const color = CommonColor.fromHex(hex).rgba;
+		const color = BaseColor.fromHex(hex).rgba;
 		return new Color(color.r, color.g, color.b, color.a / 255);
 	}
 }