setBackgroundColor, doesn't handle alpha properly, lets just use turbowarps version of the func lol

Author: FreshPenguin112

src/RenderWebGL.js

@@ -473,19 +473,22 @@ class RenderWebGL extends EventEmitter {
      * @param {number} red The red component for the background.
      * @param {number} green The green component for the background.
      * @param {number} blue The blue component for the background.
-     * @param {number} alpha The Alpha component for the background. (0-1)
+     * @param {number} alpha The alpha component for the background.
      */
-    setBackgroundColor (red, green, blue, alpha) {
+    setBackgroundColor (red, green, blue, alpha = 1) {
         this.dirty = true;
 
-        this._backgroundColor4f[0] = red;
-        this._backgroundColor4f[1] = green;
-        this._backgroundColor4f[2] = blue;
-        this._backgroundColor4f[3] = alpha ?? 1;
+        // WebGL will want the color to be pre-multiplied.
+
+        this._backgroundColor4f[0] = red * alpha;
+        this._backgroundColor4f[1] = green * alpha;
+        this._backgroundColor4f[2] = blue * alpha;
+        this._backgroundColor4f[3] = alpha;
+
+        this._backgroundColor3b[0] = red * alpha * 255;
+        this._backgroundColor3b[1] = green * alpha * 255;
+        this._backgroundColor3b[2] = blue * alpha * 255;
 
-        this._backgroundColor3b[0] = red * 255;
-        this._backgroundColor3b[1] = green * 255;
-        this._backgroundColor3b[2] = blue * 255;
     }
 
     /**