libs said:oooo have you tried
peering at the side of it to see if you can see the colour there?
holding it up to a v bright light - preferably a lamp, the black spots in front of your eyes fade after a while
scraping the top layer away with your nail to see if there's anything underneath?
putting it on a black background to increase the contrast?
taking a photo and making it a negative?
not that I've done any of these ..... you do make me giggle libs * now goes off to try all these*
good luck hun