If you must use spray paint, just mask off the wheel well area and the surrounding areas on your car with newspaper and tape.
But, I would recommend using G2 paint. You can get it at http://www.tirerack.com
although you can find a cheaper price if you search around :google:
BTW, G2 paint goes on with a brush
Edit: here's a direct link to tirerack:http://www.tirerack.com/brakes/g2/caliper_paint.jsp
It is look good after paint??
Will I mess it up cause I never did it before??
Can I get G2 at Pepboys or stores??
How many time I can use it??
And thanks for your advice, I think I know how the switch light by myself now, you saved me an arm and a lag XD
But I still dont know how to switch the bumper lens = =