I don't know if this website has been posted, if so sorry about a repost. It allows one to play with the striping colors on the GT500. While I don't think the colors are official, it at least let's you play with them.
http://www.spectrummarcom.com/mustang/cobraPainter.html
http://www.spectrummarcom.com/mustang/cobraPainter.html