Highlighting extreme edges is a fine art, to pull it off well you need to ado at least two passes on the model. Always use the base colour and blend with a lighter colour for the first pass (50/50 Yellow/White, or Bone/White, etc) for the first pass; go over all of the model, each panel/section/etc.... making sure to keep the highlighting to the outer most edges only (about 10% of the panels surface area) and on an engel that would naturally be hit by light. For the second pass, add more of the lighter colour (about 3:1 ratio or more) and only highlight the very edges of the first highlight (about 1% or less of the total panels surface area), often White can be used on its own if your going to do any sparkling effects on very predominate or rasied corner edges. Things to remeber are that the paint should be very thin, so that you get a good blend, and that this technique can be used with any colour, as lonag as you are carefull to not change the tone of the original colour with your lighter blends (Example,,, don't use yellow to lightenn Blue, as it will end up Green,,, white is better. And don't use white to lighten Red as it will end up Pink,,, yellow works better.)
For your gems or jewels I would suggest using Reds,,,, not because I'm a Saim-Hann freek (although I am) or because red makes anything go faster (as we all know it does); but because red is actually a good offset colour for Blue, Yellow, and Bone, and I thought I saw some Gold on one of your models and Reds go well with gold as well.
Hope that helps, Cheers and Happy gaming.