I have never had floor registers, so I cannot help you there.

I DO paint mine to match the walls they are on... usually with the same paint as the walls. No high temperature.... just regular latex.

did you know you can buy oak ones?

Yes, I know that I can buy oak registers; however, I'd like to keep the metal ones.

How about antique bronze or just bronze? If you want the registers to stand out and you have black in the room, how about "wrought iron black"?

you could spray on a layer of flat or satin finish too if you like the brass look.

I have dark brown ones with my red oak floors. Not the greatest color maybe but they are pretty much hidden behind furniture so it doesn't bother me. For my room I'd prefer a matte black since I have other black metals (including a big black wood stove) in the room. I don't think floor registers need to match the color of the floor.

I just put in an oak floor and had the register problem too. I use magnetic air deflectors, so it was easier to stick with the metal register covers.

My oak has a light stain on it called "Butterscotch". It's not quite the same as the natural but it's very close.

I sprayed the registers with Rustoleum Ultra Cover 2x in Khaki. I'll try to get a picture for you tomorrow. I think the registers blend into the floor nicely.

If the paint does not hold up I'll get the oak covers and glue on something for the magnets to stick to, but I've painted other metal registers in the house and so far they are all holding up fine.

I came to this thread with the same issue as you. I am going to paint my metal registers. We tested out the oak ones and hated them. They stick way up and are a huge toe-stubbing hazard.