Color change in diamond without losing luminosity? :-( Please Help

Hi, I really appreciate if somebody can answer this question:
I have a diamond image, which obviously has different shades in it, it actually has dark, like dark brown shades, which i want to change to lighter smth like light yellow, i tried replace color, hue/sat//light but the effect is not realistic like an actual diamond looks, it is loosing its luminosity. i even tried with magic wand tool, by selecting each darker part and changing color, but it does'nt look realistic either. I would be very grately if somebody could help me with this. I m using Photoshop 7.0
Here is the image link i m editing:
http://img143.imageshack.us/my.php?image=r2064chd10kygalleryex0.jpg
Thank You in advance.

I looked into your delema, and I tried my hand at a solution.


The method I used was the "variations" command
I changed the midtones to more yellow a few times, then I used the "fade" commade with a setting of about 30 percent with the "screen" blend type.