BMW paint codes can be found on the underside of the hood and strut tower. The codes are mostly made of three numbers (like 448) or a letter and two numbers (like A50) and are usually on the bottom left or right corner of the sticker.
You can also find your car's color code by providing the last 8 digits of your VIN to the parts department of your local BMW dealership and they will be able to tell you what the color is.