On the white iBooks it's a clear case with white paint on the inside. You will need atleast a 80% isopropyl alcohol to put on the inside. It will desolve the paint and you can use a soft cloth to remove the paint. After that you can paint inside.
If you have high quality paint and clear coat you can paint the outside of the case, but due to the wear you will get with a laptop, painting the inside part is preffered. There are some mod guides on painting iBooks in the External > iBook mod guide section.
Quick Link to one such mod guide: http://www.macmod.com/content/view/37/2/