Choose one of the known schemes from the list after the "Reset To"-Button, then press this button. At first, you will get a preview. The setting is installed when you finally press the "Accept" button. It may be required to reselect the current method in the SystemBrowser.
You can also define your own coloring scheme there.
Please notice that your changes are only valid during the current session, unles you press the "Save" button. Then, the current settings will be used as default in the future.