Use less bright colors for output

[waj]

This might be seen as a silly thing but it could be actually pretty annoying sometimes. I know some terminals have settings to ensure minimal contrast but I think it's better not to rely on that configuration.

Because we cannot aim for any background color, I just tested with the extremes: black and white. For each case, here is how it looks before and after the change. Bright colors look great on dark background, but I can barely see WARN on the light background. BTW, bundler uses the same colors.

[straight-shoota]

How color codes are reprsented depends on the terminal's color scheme, so we shouldn't bother about specific details that might already look different on the next machine.
But using all colors from the same family (non-light) seems reasonable.