Premultiply background RGB values if alpha is used

x.c

@@ -784,9 +784,15 @@ xloadcols(void)
 	/* set alpha value of bg color */
 	if (opt_alpha)
 		alpha = strtof(opt_alpha, NULL);
-		dc.col[defaultbg].color.alpha = (unsigned short)(0xffff * alpha);
-		dc.col[defaultbg].pixel &= 0x00FFFFFF;
-		dc.col[defaultbg].pixel |= (unsigned char)(0xff * alpha) << 24;
+	dc.col[defaultbg].color.alpha = (unsigned short)(0xffff * alpha);
+	dc.col[defaultbg].color.red =
+		((unsigned short)(dc.col[defaultbg].color.red * alpha)) & 0xff00;
+	dc.col[defaultbg].color.green =
+		((unsigned short)(dc.col[defaultbg].color.green * alpha)) & 0xff00;
+	dc.col[defaultbg].color.blue =
+		((unsigned short)(dc.col[defaultbg].color.blue * alpha)) & 0xff00;
+	dc.col[defaultbg].pixel &= 0x00FFFFFF;
+	dc.col[defaultbg].pixel |= (unsigned char)(0xff * alpha) << 24;
 	loaded = 1;
 }