if you want a brighter bulb than the one you have now, just get a bulb that is rated with a higher wattage. dont go too high, or you will draw too much current and possible burn out the wiring too the bulb, if the fuse doesnt blow first. you also may end up making some of the other lighting wired with it a little dimmer.
your other bet is to just run new wiring to the spot and put a brighter bulb in that is drawing power from a new source.
the final solution would be to change out the piece of plastic that the light is shining through to the desired color.