Saying that nobody has replied to this, I will just throw out a couple of suggestions. Its only possible to change the colour scheme on the app. So its either a case of finding a way to run the app on your PC. Or using external methods to change the colour scheme on the AW website itself inside your browsers.
Two ways to do that.
1. You could use an extension such as
External Link/Members OnlyI have used this and its great.
Or
2. You can change the default background to all websites. To do this go to Firefox and select Options > Content > Colors and change the background colours.