please help on painting already painted fiberglass fenders

So I got a killer deal on some glass works fenders but they are already painted forest green. How should I sand the paint off? By hand? By sander? What grit? And what stages of grit? Trying to make them look good. Also my truck is white if that answers any questions. Thanks!

 

Since it's already painted you should only need to scuff it up for the new paint to stick. I used 600-1000 grit and did it by hand...

 

Nice though I would need to take all the paint off so the dark green wouldn't show in the white

 

There is no white paint under the green, when you see raw fiberglass fenders that are white it is not white paint that is just the white gel coat that seals the fiberglass. Your best bet is to scuff them, fill any chips etc and then paint them white.

 

No I'm saying my truck is white I'm saying if you could see the shade of green under the white cost of paint I'm gonna put.

 

maybe put a white primer on first, should help hide the green.