If you are buying from Michaels, just pick out some stuff you like and ask the florist if they will bleed. I used to work at one and I had all of the flowers memorized whether or not they are fine in water. People don't want dyes all over their loved one's headstones and such, so I just transferred that over to aquariums. I haven't had an issue yet.
And of course make sure they have no metal parts. They will fade gradually, as any of the fish-specific stuff would. But, if it is a quick fade, then first off that florist was a moron and second, get it out!