@aqib: usually before paint "astar" (cant rem the name of the chemical at this time) is applied,this is the greyish colour chemical applied to make ground for the paint,when this is applied,you can apply any colour of paint and it wont have the effect of what colour it was before.
So like if you got silver/chrome rims and before the paint you apply astar,you wodnt need to worry about the previous colours effects coming into the new colour.Just apply atleast 4-5 clear coats of paint with 1-2 clear coats of a good quality/imported laquear on top of it.