var magentaRed:int = 255;
var magentaGreen:int = 0;
var magentaBlue:int = 255;
var magentaCSS:String = RGBToCSS(magentaRed, magentaGreen, magentaBlue);
trace("magentaCSS: " + magentaCSS);

function RGBToCSS(r:int, g:int, b:int):String
{
	var hex:uint = r << 16 | g << 8 | b;
	return "#" + hex.toString(16).toUpperCase();
}

// OUTPUT
// magentaCSS: #FF00FF

AS3 RGB Colour to CSS Colour (String)

css, color

ActionScript 3