Loving the yellows, going lime with the Dark green as accents, reds look good too ...
I think the dark Blues need a bit of light injected into them maybe take a bit from the lighter blues and the purples look great. Im going to struggle with Sapphire as well, I have loads of gorgeous Darks but not so many lights!
Its all about lights and darks ... Maybe bring up some pics of real gems on your laptop and look at the kinds of colours involved ... you might be surprised... But if there is a flash of (for instance) dark green in a Citrine, or Violet in a Sapphire ... make sure you reserve that colour for the smallest units within the block!
But in the end its just about the sense of gemstones ...