White Pvc

Can I paint internal Mahogany coloured PVC window frames white? If so how do I prepare & what type of paint?

Yes. Basically all companies do.
Procedure:: First wash them clean with solution of TSP and water and let that dry. Scuff surface-go over it with120 grit sand paper just to "get some scratches in it". >These scratches give the paint a "mechanical hold" to the surface like a hook would grab into a crack.<
Then get a quart of "plastic primer"And that is what it is called"" and thin it out 10% with paint thinners recommended for product(it is an oil based product). Brush that on(with a bristle sash brush angle cut).
Let that dry at least 2 days.
Then use Latex eggshell(thin out a bit with water). (Use a polyester sash brush angle cut). //

Thinning out makes the paint go on better, smoother, stick better and gives better finish.