Grey would be a little redundant don't you think? I think a special mineral needs a special color.
We have lots of glowing elements. Deut for instance, it glows when it's life reaches a certain number. VIBR has the same property.
Edit: :( I thought this would be implememented in the 82.0 update.
*extra bump* I feel paranoid :L
Thanks, I think I should keep a tally.