leather paints and dyes

Does anyone out there know about colouring or painting leather?

I have what was once a blue collar with gold bits but is now faded, and a black collar that I'd like to decorate in silver. I am wondering if it's possible to dye the blue one back to a truer blue, and what sort of paint would be most durable to create a pattern on a thick leather surface. Any tips or links would be appreciated!