Maximize/Minimize/Close buttons are all greyed out

Hello. Ever since a few days ago, the green, yellow, and red maximize/minimize/close buttons at the top left of every window have all been greyed out. They're all still completely usable and they do what you would expect them to do...there's just no color in them anymore. This is happening for all applications.

I'm not really sure what's causing this. I don't remember exactly when it stopped working or what happened right before it, but it may have started happening right after my computer shut down, possibly from overheating (My friend was trying to be funny and opened the application window in finder and then pressed Cmd+a followed by Cmd+o --- To open all of my applications. We watched it chugging along for a while and then the screen just went black and the computer turned off). I don't know if that would cause the problem, I'm not really sure why it would.

I tried a google search but came up empty handed. Any advice on how to fix this would be much appreciated. Thanks.