Dope sheet and graph editor are kind of "dark" This strange thing happens when some books falls on my keyboard. It doesn't affect to my workflow at all but it's really annoying. 

As you can see, it's seems like i have switch off a bright option or something. I can't explain this very good and neither know how to search for a solution.
This only happens on that project. I've tried reseting blender and opening other projects but they looks cool.

Anyone knows the shortcut or the key i missclick or it's other kind of problem?
Thank you
Use "Alt+P" to clear the preview range.