From FAQ

What do the little green/gray/red squares mean?

You can see a member's reputation easily by the number of "gems" that are displayed below their avatar, on each of their posts. The Green gems indicate a positive reputation, the gray gem indicates an unknown reputation, and red gems indicate a bad/negative reputation.
Color Green (Whether in a traffic light or on a gem) is not always bad

Having said that, if you really like the color red, I am sure many would be obliged to help you with that