Colour Photos on Metal

I’m interested in the process of getting a full colour image
transferred onto metal. A company called Rockaloid make a (black & white) photo emulsion
“designed for applying to any material, in any darkroom”… “print on
all kinds of interesting materials like wood, glass, ceramics,
plastics, chinaware, fabrics, metals, stone … an egg”.

But how about colour? I’ve seen some jewellery featuring little
coloured photo-images on metal. Does anyone know how that’s done?

B r i a n � A d a m