Alright, here goes on the painting department.
How to paint a jewel- Start with a very dark coat of the color you like- darker than it would normally be. Add a second coat, covering 2/3s of the jewel, leaving the lowest (in theory) third or so of the jewel the original color- make sure that it is not a completely straight line, but either arced or at an angle. Then, for the third coat, cover a third or so of the jewel, leaving sections of the previous colors, having this color be the color you would like. Finally, add a slight touch of white to the highest part of the jewel. Proceed to experiment on this theme.
Now, if you would like effective metal that will go with the blue and white theme, then my question is do you want a blue-tinted armor or a normal, silver armor? For blue tinted, start chainmail, water down regal blue (very watered down) and then wash, highlight again with either chainmail or mithril silver. For black, do the same, except with black ink, or chaos black.
I think that the blue color scheme should look nice, for the white, would you prefer a 'softer' white, which means more of a warm, cream-ish tone, or a 'harder' white like the white you find on this page? If you prefer the 'soft' white, start with some really light brown (graveyard earth is my favorite), do 2nd highlight in bleached bone (a wonderful color), and the final in skull white. If you like the 'hard' white, then do fortress grey, fortress grey/skullwhite mix, and final stage highlight strait skull white. Hope that helps!
"...in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.”