I manufacture small aluminum parts for motorcycles. Some of these parts are chrome plated, but chrome is not always the best application, because the placement of the part on the bike could cause sunlight to reflect into the rider's eyes.
I have had good luck with both powder coating and anodizing from outside facilities, but I am looking for a finish that I can apply. I have ovens for curing or preheating and facilities for spraying.
These parts are engraved, and an ideal application would be to be able to apply multiple colors, either by masking and spraying, or even brushing. Ideally, some applications would allow for intricate work and be applied after chrome is selectively masked and sandblasted. This is an art-type application done for satisfaction more than monetary gain, but making small investments in equipment is not out of the question. Not needing to prime the material is a definite plus, as is minimal surface preparation. As this is for a motor vehicle, UV protection, heat and gasoline resistance are all of prime concern. T.G.
I don't know what you are painting, and it doesn't really matter. The important thing is that the substrate be clean before painting. No matter what you apply, it must be over a clean substrate. Your problem is complex, but I can give you some options for color coating aluminum.
Adhesion to bare aluminum is enhanced by using a primer. The traditional primer for aluminum used to be a phosphoric acid activated vinyl wash primer. This can be topcoated with most materials. However, this material has fallen into disfavor because of environmental concerns. Epoxy primers adhere well to bare aluminum. The two-part epoxy polyamide is best, followed by a one-part primer such as an epoxy ester. They can be topcoated with all materials. Thermosetting acrylics are also suitable for painting bare aluminum. Your best source for all these paints is an industrial or automotive paint supplier rather than a trade sales paint store.
Another approach would be to paint over anodized aluminum, which is an excellent paint base. You can use any number of automotive grade enamels as color coats over the anodized aluminum.
A third approach would be to use a non-chromate conversion coating on the aluminum. These conversion coatings are excellent paint bases and could be color coated using automotive grade enamels.