Hi Frea,
Welcome!
I'm sure that David will give you some  more knowledgeable info on this, but in the meantime I think there have been a couple of threads here about fluorescence, some with photos that show it better than I can describe - try a search?

I don't think it's always bad and can sometimes even make a diamond look whiter. I have a couple of diamonds that fluoresce quite strongly and I think it's really cool! I read that very strong fluo can make a diamond look slightly milky or oily sometimes,  but I've never actually seen one that is negatively affected to that extent.

I'll give David a shout, so you can have a professional answer! 

Jen

By the way, excuse me for not mentioning this earlier, but I want to extend the warmest of welcomes to our new member frea!!!

thanks very much,
 I had a long look at the posts last night (Im in Aus- so diff times)
 and I realise florescence is not really a bad thing- maybe it's more personal taste..