1) use oil base sealer / primer as undercoat (white) to cover the original color. Just look at it as a kind of white paint. The sealer also makes it easier for you to paint the color on it. If the original color is too dark, you might have to prime it twice to fully cover it.
2) use oil base paint to paint whatever color you like. Just choose your color and they (Home Depot or Canadian or ...) will tint it for you.
if existing paint is water base / latex, use latex sealer and latex paint
if existing paint is oil base and you want to use latex, you will have to sand it first, or I heard someone say you can find a kind of oil sealer on which you can use latex paint.
2) use oil base paint to paint whatever color you like. Just choose your color and they (Home Depot or Canadian or ...) will tint it for you.
if existing paint is water base / latex, use latex sealer and latex paint
if existing paint is oil base and you want to use latex, you will have to sand it first, or I heard someone say you can find a kind of oil sealer on which you can use latex paint.