I don't think there is a built-in method for changing the colors, but please contact our Support team if you want an official answer.
That said, there are plugins that let users change CSS rules for specific sites, which might be useful for your developers. One example is Stylish for Firefox.
Note that we updated the UI in our 6.0 release, to make it generally easier to use (and to look at). You might want to consider upgrading, to see if your developers are happier with it.