It has no efect all. Unless you painted a very nice original paint job a different color or if you paint it pink with green polka dots. e.g. A very nice original matching numbers ride is worth a premium as it is. If a car has to be painted it will not fit in that catagory and it will be worth more painted.

It all depends upon the buyer. Some people might like the red with black rally stripes look more than they would the original color. Plus, if the paint job you have now was custom that could even increase the price of the vehicle. While some people like a car based on originality others like a car based on looks.