Scanline Effect, Now Colours Appear To Be Washed Out??

[lettuce]

Im using Aaron Giles's scanline effect, however i have notice that when you are using the the scanline effect (and maybe others) that the colours appear not to be as bright and crisp and appear washed out as oppossed to when not using the scanline effect, and also the brightness/contrast seems to be alot lower aswell, but this can be changed within mame. Does anybody know why the colours are 'washed out' when using the scanline effect, and is there away to get the colours back to being bright, clear and crisp??