I was having the same problem. There is no defualt botton to change the W7 colors back to defualt color settings, but I found a trick (by the grace of God) by accident. FOR DEFUALT SETTINGS:
1.) Leave open WordPad. Type something in it. (Even leave one IE window open)
2.) Go to Restart Computer and Select it
3.) Windows will not shut down but warn you you have WordPad or IE opened.
4.) Don't press Force Shut Down
5.) Select Cancel
6.) Now go back into Personalization >> Windows Color and Appearance
7.) Click Advance Appearance Settings
As odd as it is, by canceling Force Shutdown, you will see that it goes back to Defualt Colors. "Apply" is greyed out, so change the black to any color and back to black. BOOM!!!!!!!! "Apply" will now beable to click to save the Defualt Color Scheme.
Please no "Thanks" to me but thank God for me, please? I was very frustrated I could not undo my colors I chose that I love, but my colors messed up Windows by not being able to see words due to color conflict, contrast, and confusion. Windows defult colors are set up for a purpose, so we can read and see everything on our computers or on the web.
I hope this helped. God bless!