You could scuff and use duplicolor lacquer spray paint in LIGHT coats. Also make sure your surface is free of finger oils (sweat), grease, wax and dirt. A wash with soapy water and after drying, using rubbing alcohol, wet one rag and wipe the surface to be painted drying the surface with a dry clean rag, your surface should be cleaned properly for paint now.Since your trying to cover a neon blue with orange (just about opposites) you'll need to hit it first with ONE wet coat of gray primer. Imagine you can only see in black and white, ideally you want your primer shade to match your orange color in gray scale. ie, if your orange is very bright then look for a light gray or white primer/surfacer, if it is a dark orange then you can start with a med gray or black primer/surfacer. Primer/surfacer fills in the scratches that the anodize didn't fill in which you can sand before the orange is laid down. For the orange if it is in a spray can, being a metallic, you want light coats maybe three to five of them and you want consistent speed movement with each consecutive pass being about 1/4 to 1/3 of the fan spray width. To see what the fan spray is, hold a piece of scrap paper verticle about 6 inches from the spray can and without moving the spray can, spray the paper for 1-2sec. That line that it just sprayed on the paper is the fan and you want to overlay your passes by 2/3 to 3/4 of a fan. Light coats is key because you are overlaying your fan spray. By overlaying you can eliminate "zebra stripes" which are actually just dry edges where the metallic does not lay down but stands up trapping more light and appearing darker. It's very important for proper paint adhesion to let the paint "flash" between coats. The flash time lets the reducers to evaporate out of the paint film. Flash times should be 2-3 minutes for light coats and 4-6 minutes for wet coats when the paint surface is at 70F/25C. You can use a heat gun/hair dryer from behind the panel to warm the panel thus speeding dry/flash times. You can also use a heat lamp aimed at the same side you are spraying because the heat lamp creates infrared light that penetrates the paint and cures it from the inside out. With either method of curing, DO NOT exceed 160F on the panel temperature or you'll burn the paint film turning it a darker/browner color. Heating the panel will cut cure/flash times in half, but you will also have to spray faster and heavier with the same overlap to avoid dry edges aka "zebra stripes". Using the hot air source on the same side as the fresh paint will "close" the outermost part of the paint layer trapping solvents within and causing the paint to fail at a later time (read blushing, solvent pop - cratered texture similar to that pizza faced kid you knew in high school, or delamination - when the paint just peels off like a bad sun burn). The chemistry of the paint being a plastic film when dry will trap in some heat but not much, maybe 1 or 2C. Clear coat isn't needed unless the base coat has to tolerate large amounts of UV ray exposure or outdoor environment (acid rain/dirt/bird poo).
That's the best i can advise without spraying it myself, being a professional autobody tech of 14yrs and a certified PPG auto painter of 5yrs. Your other option is to polish the heatsink, being aluminum it's relatively easy to polish compared to other metals. You can wetsand it with 320 grit sandpaper that's meant to get wet and progressively move to finer grades of sandpaper (320, 500 or 600, 1000 or 1500, 2000 or 2500) and then with a fine steel wool pad and some billet aluminum polish begin rubbing the aluminum using a moderate to heavy amount of polish. The shine should come up quickly with the fine steel wool, then finish the polish with a dirt free cotton rag/cloth/towel. (a cut up new fruit of the loom white cotton t-shirt works great for this.
Good luck with it and remember patients is a virtue with painting.