Check "K9STH's" site. Glen gives the mixing requirements for Heath paint color. But be aware, Heath used several different shades of "Apache Green" for their equipment. And YES, do scrub/scrape down to bare aluminum. THEN use primer. A couple of days to dry is a good idea, THEN use the proper color spray, usually two coats will be sufficient. Also, be aware that some larger "Wally World" megastores may have a spray paint that can be very close to the original Heath color, and may be acceptable. (And less $$) There has been good advice above; I don't know about your SB-220, but the case of my SB-200 is GRAY, not HeathKit "green."