Hmmm .... I used to colour aluminium (I'm Australian so that is how we describe the metal) components for my 470 boats. I was a good 470 sailor but didn't crack the Olympics. Australia has won many gold medals in that boating class.
But I would have the alloy parts, after I had cut them into the shapes I needed, anodised. Its an electronic bath which puts a strong colour very strongly onto the metal. I think Apple use that process for their alloy phone cases. At least, they used to. Probably the iMacs etc. too. In Australia, its become tough to have things anodised these days though - due to the toxicity of the fumes from the process. It used to be a very cheap thing to have done, by small businesses.
If you can find a business that anodises small jobs, it would produce an awesome finish.
However, such a coating would change the internal dimensions a little bit. I doubt that would effect things, but then, on an old machine, it would still make access tighter, for instance, around the power supply etc.
Typical colours back in late 1970s and '80s for anodised alloy parts, were gold, blue, black, and a silver colour (perhaps what Apple used). If you look at alloy masted boats and yachts, you might see some gold masts etc. Blue is much rarer, but still around. Black and silver was popular for yacht masts. The anodisation prevented oxidisation of the alloy, and also was very strong, chipping of the coating was unknown to me, but possible.