I wondered if any of you have actually ever seen a chameleon diamond or own one. 
I like the idea of it changing color but I believe its a bit different then say alexandrite or other colour changing stones that shifts colour between florescent and natural light.   

I understand that Chameleon stones change with heat and or light and darkness but does it take extreme heat changes or long periods of time in darkness or is more or less instant?
Also how large is the color shift?  Is each stone different?  Is one more or less expensive then the other?
Any GIA report on a chameleon diamond didn't include any of these things so I wondered if there were even important!

Thanks!
Flyingdiamonds

David will probably add more, but here's a starter for 10 at answering your questions:

1. Change is gradual - certainly nowhere as fast as an alexandrite or colour-change sapphire. The mechanism by which chameleons change colour is also such that unless you heat them quite a bit (200 °C or so) the colour change will take some time to reverse. My wife's green/yellow chameleon takes a couple of hours in darkness to "reset" itself.

2. Mine goes from light yellow (no green; about S-T) to light green (no yellow as per GIA report) in about 20 minutes in sunlight and up to two hours in artificial light. From what I've seen both the time and the intensity of colour change are very much individual to each stone. I don't think - despite a few ads on eBay asserting the contrary - that chameleons are particularly valued, nor that the value depends on the intensity of the effect (possibly excepting extreme cases; I suppose if you had something that went from vivid green-yellow to vivid brownish-greyish-green...)

I am curious, and I think I have posted this question before....but how does the GIA know to test a diamond for Chameleon properties?  Is this something they do on a regular basis with a colored diamond?