What's the best method for painting InWall speakers?

I'm going to be helping a friend install some inwalls, and she wants them to blend as much as possible. I'm thinking just regular old rattle can spray paint, maybe with a clear coat unless there is some reason I don't know of to not do this.

Airbrush or a 'power painter' is not really an option as I don't own that stuff and won't buy it just for this project