Don't paint receptacle covers!
It's simple. The covers should be removed before the wall around a receptacle should be primed and painted.
Painting the cover and receptacle while on the wall is not a good thing to do for many reasons:
1. The cover plate is essentially glued to the wall and the receptacle. To remove it requires something sharp. Damage can be done to the wall and/or receptacle. And a slip could be made inserting that sharp object into the receptacle itself. Damage is not only possible, but probable.
2. The holes of the receptacle can be filled with paint. I have seen them so filled you can hardly see that a receptacle is there. In the case in this photo I was unable to insert my testing device to see how the receptacle worked.
3. But also, paint is latex, which IS NOT conductive. When a plug is pushed into the receptacle paint can also be pushed inside. The inside of the receptacle IS conductive. When a non-conductive material is pushed against a conductive material resistance will happen. Resistance causes heat. Heat and electricity are not a good combination. Yes, receptacle fires can occur.
4. Once a color is on the wall, and if the cover plate and receptacle have already been painted, if the color of the wall is to be changed the temptation is to paint the receptacle again the new color! That adds difficulty and potential danger, to difficulty and potential danger.
My recommendation: take a moment to remove the cover plates before painting. Tell your painter to do the same. When receptacles are painted such as the one in the photo it is ALWAYS best to remove and replace everything. Be careful! The difficulty and potential danger still exist!