Please Help with Graphite2 Theme

This is my first time requesting help, and I'm not sure if I post this in the correct place, so please forgive my ignorance.

Can someone please help me find where to change the font colors in the Graphite2 Theme.  For instance, under "Activity", All, Mine, and Friends blend into the background.  I would like to change those words to black.  However, I can not find the code to do so.  Can anyone help?  I included a picture just in case I didn't explain myself clearly.

Thanks in advance.image