Can I paint a load center cover?
That is fine. The Electrical Code is silent on the issue, except for NEC 110.3B, which requires you to obey the unit's labeling and instructions.  So if they do not disallow painting the panel, then have fun. 

Do not cover up any labeling or numbering, and do not paint the breakers themselves. 

If you have a panel with no door, and you don't want to be looking at breakers, then contact electrical supply houses (not retail stores) until you find an authorized dealer for that brand of panel.  Ask them about panel covers with doors, or retrofit doors.  Paint the door. 

The only exception is if your panel is the CH type.  Cutler Hammer's choice of color is pure perfection.  To make it match,  paint the rest of the house that color! :)