private static ColorUIResource parseColorRgbOrRgba( boolean hasAlpha, List<String> params,
		Function<String, String> resolver )
			throws IllegalArgumentException
	{
		if( hasAlpha && params.size() == 2 ) {
			// syntax rgba(color,alpha), which allows adding alpha to any color
			// NOTE: this syntax is deprecated
			//       use fade(color,alpha) instead
			String colorStr = params.get( 0 );
			int alpha = parseInteger( params.get( 1 ), 0, 255, true );

			ColorUIResource color = (ColorUIResource) parseColorOrFunction( resolver.apply( colorStr ), resolver );
			return new ColorUIResource( new Color( ((alpha & 0xff) << 24) | (color.getRGB() & 0xffffff), true ) );
		}

		int red = parseInteger( params.get( 0 ), 0, 255, true );
		int green = parseInteger( params.get( 1 ), 0, 255, true );
		int blue = parseInteger( params.get( 2 ), 0, 255, true );
		int alpha = hasAlpha ? parseInteger( params.get( 3 ), 0, 255, true ) : 255;

		return hasAlpha
			? new ColorUIResource( new Color( red, green, blue, alpha ) )
			: new ColorUIResource( red, green, blue );
	}
Syntax: rgb(red,green,blue) or rgba(red,green,blue,alpha)
  - red:   an integer 0-255 or a percentage 0-100%
  - green: an integer 0-255 or a percentage 0-100%
  - blue:  an integer 0-255 or a percentage 0-100%
  - alpha: an integer 0-255 or a percentage 0-100%
flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java