I don't there is such a thing as a chromatic primer. The process I think you're referring to is called chromatic conversion coating. It's a chemical process, not a paint application.
Presumably, you're asking this because of magnesium. As far as I know, Dymag will do it. Don't know if they'll only do the conversion coating without the painting afterwards.
You can also try
Surface Engineering Association, which list a number of companies that perform this process. I remember speaking to Ingram&Glass about this a couple years back. The bloke I spoke to was Micheal Glass (MD) at 01483 415 262.
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