I would think powder coating would be best. One can powder coat a prop so why not an anchor? Very wide choice of colors.
I have painted large parts of some of my anchors w cold galvanize spray cans. So easy to touch up. But seldom needed. It's very much like Navy gray it visually blends right in w real galvanize but it definitely is different than the hot dip galvanize. One could just paint w cold gal the whole anchor .. then the color would be uniform. Get it at a good price in paint and hardware stores under the Rustoeliun brand .. >$10.
What's the reason that you would want to paint an anchor? Make it look nice? Control rust?