Sometimes sites use a color scheme you don't like. I can't stand looking at white text on black background; others love it. I like my black text on yellow graph paper theme, but not everyone has 20+ years of staring at engineer's pads. Nobody likes gray text on gray background, except John Gruber.
Just drag the javascript link below to your browser address bar, and click on it. It'll change every element on the page to black text on white background. Or you can edit it, and change the "white" and "black" at the end to the background and foreground colors you want.