You can change the theme in Office by clicking File > Account page in any Office product with the exception of Outlook. In Outlook, Click File > Office Account to change the theme.
There are three themes available in Office 2013:
White - Default
Light Gray
Dark Gray
For more information, view the page below:
Change the Office theme
The trouble is it does not stay that way.
I just cannot believe MS did this. I have to have it at work and I HATE it. I wish I could go back to 2010. For the first 3 months the theme stayed at dark grey. Outlook and Word open having defaulted to dark gray (which our IT guy had to set on the server
so that it goes out to everyone) but on opening a document it reverts to the disgusting WHITE and then I have to go into File Options and change it back to dark gray EVERY DAY. It's just ridiculous. I, like everyone else, do not for the life of me understand
what MS were thinking. Even worse than the theme is the QAT. My QAT runs across the whole screen and there's no colour. It's pathetic.
MICROSOFT, please listen to what everyone is saying and do something about this.