From a marketing perspective, black tends to be a safe colour to choose because it's the least offensive and most subdued.
From an manufacturing perspective, if a pigment is involved (such as the case with paint, colouring plastics, or powder coating metals), black tends to be the safest and cheapest colour to go with for a number of reasons:
- black pigment is cheap (typically carbon black)
- carbon black is immune to fading and discolouration
- carbon black protects plastic against UV degradation. This is why black nylon zip ties exist in addition to the uncoloured (white) nylon zip ties.
A popular, good white pigment that doesn't fade and protects against UV is titanium dioxide and tends to be one of the pigments in higher demand thus making it expensive. It's also just more expensive than carbon black by default.
So the pigment is the likely explanation if the exterior of the camera is mostly plastic. This is why if you need to colour a plastic something other than its native colour, black tends to be the default.
If you choose to make your camera exterior out of metal, well that's just expensive to begin with. If you use paint or powdercoat, you are back to the pigment argument.
If you choose to colour your metal without involving pigments then that leaves plating and anodization. I don't know of a white plating or anodization (though I have never gone specifically looking for one) but black ones are common.
But if your case is already metal and you don't want to use pigments then perhaps you could just give it metallic finish Well that might involve more material costs since it could involve nickel or chrome if steel, brass, or copper is involved. Or perhaps just plain if it is aluminum or magnesium. And then would need to it to be sandblasted, brushed, or, dare I say, polished to a mirror shine. And you do see this often...on the few metal parts on the exterior because metal is expensive. You might see it more often if more cameras had significant metal exterior.