You might want to try adjusting your contrast, as well. Contrast is the setting that determines the difference between light and dark images on the screen.
Since using component cables is a different input on the TV from the composite cables, it is very likely that both inputs do not have the same display settings (brightness, contrast, tint, color, possibly more depending on your television). A good test would be to go to another input, such as your television input or another device on composite and writing down the numbers that your display has for those values, and then adjusting the component input to match. You'll want to pick the positions that give the best picture, but those will be a good guideline.