I would think that it would mostly depend on the ear ring type. If they are the standard sterling silver hoops or barbells, it wont draw too much attention from the costume, but if they are brightly colored or huge they probably will. They do make clear plastic studs that you can put in.
I have an industrial, and a conch in one ear, and 2 lobe piercings in each ear, I also have to paint my ears and and put on elf ears for my cosplay. I will probably take everything out except the conch (just cuz it's a pain in the ass to take out and put back in). Paint shouldn't be an issue unless your piercings are brand new, even then anti-bacterial soap should be able to clean it out just fine. For safety sake though talk to your piercer first.