Reset System Window Background Color?

My daughter has accidentally changed the background of all her systems windows to white. How do I reset to the default (usually white and grey). Example, systems preferences and iTunes all have a white only background. She has a MacBook, running Yosemite 10.10.3.

I have tried all of the Systems Preference I can think of, and compared all settings to my MacBook Pro. I can't find where to fix this.

A fix, or reset to default settings would be great. I can't figure out how to do either.