If you're hoping to remove paint from vinyl siding, there's a way to do it. Perhaps you lucked out and found previously-used siding at a recycling center and are hoping to return it to its original color. If it's already installed on your home, your options are to remove it first or remove the paint while it's up.
You have a number of options open to you. Try old-fashioned, petroleum-based paint thinner. Some say gasoline will do the trick as well. In both of these cases, be sure to wear protective gloves, eyewear and possibly a mask. For acrylic or latex-based paint, try blasting the siding with a pressure washer or, if that fails, scrub it off with a substance removal product.