Keep this in mind too, that the lighting fixtures at the gem shows deliberately distort the color of the pearls or stones. It can make the color look much better than it really is. I've learned from experience that whatever I buy at a gem show, always looks different when I get it home.
If you are unable to move away from the over head lights, try to block out some of the light by putting your hand over the pearl. Sometimes I have to tell the vendor what I am doing so they don't think I'm trying to steal anything.
Gail