This is a bit tricky but it works on Mac as well. 
Option-drag the Defaults.xml file to your desktop to make a copy. Work on the copy!!!
Once the beginning of the code string is found, it will need to be selected to the end point, then replaced with the code provided by seyoum.
When ready to drag the modified copy back into your preferences, place the original defaults.xml file into another location or folder to protect it.
https://dl.dropboxusercontent.com/u/20203707/Audio/Cubase/Colors.pdf
I’m gone and will not be able to respond for a few days.
Take your time, work off of copies!!!
