code: public static String toColorWithAlpha(String red, String green,
  			String blue, String alpha) {
  		validateHexSingle(red);
  		validateHexSingle(green);
  		validateHexSingle(blue);
  		StringBuilder color = new StringBuilder("#");
  		if (alpha != null) {
  			color.append(expandShorthandHexSingle(alpha));
  		}
  		color.append(expandShorthandHexSingle(red));
  		color.append(expandShorthandHexSingle(green));
  		color.append(expandShorthandHexSingle(blue));
  		return color.toString();
  	}
docs: Convert the hex color values to a hex color
  
  @param red
  red hex color in format RR or R
  @param green
  green hex color in format GG or G
  @param blue
  blue hex color in format BB or B
  @param alpha
  alpha hex color in format AA or A, null to not include alpha
  
  @return hex color in format #AARRGGBB or #RRGGBB