EXCUSE me, Gemelli, but I have not posted an answer.  And, yes, I actually guessed that you were not talking about a three-stone (THAT would be too obvious and would not satisfy your desire to stump the rest of us)...  Sorry, I'm sure that you worked hard on this one, but I haven't had any quiet time to try to figure this Riddle out.  I DID think that perhpas the answer might be found in one of David's photo's of loose stones... For example, I DO remember that there is a light yellow stone that mentions disco, but again, I've not had the time to look for it.  Or, instead, maybe we're supposed to be trying to find sopmething with a lot of flourescence?  Anyway, if the answer hasn't been uncovered by tonight, maybe I'll have an hour to hunt.