Hello!
Thanks for posting on the Microsoft Community, and we're sorry that you're experiencing this issue. We have identified the source of this problem and our engineering team is working on a fix. I'll post back once the update containing the fix is released.
Thanks,
Michelle V
Office Team
Well, its been over 2 years now (3/4/16, your post to 4/25/18 now) and the problem still hasn't been resolved. I installed 2016 about 3 weeks ago and use the "Dark Gray" theme. I turn-off my computer at night and every
morning the theme resets to "Colorful."
Also, I agree with another post that the icons on the Dark Gray and Black themes should be normal colored; not white. It may look cool, which is debatable, but not very functional. I struggle to identify the icons in white. Please change them back or
at least make an option to have them normal or white.
Finally, in the "Black" theme, this would be my favorite choice except I can't use it because of the poor color scheme of the reminders in Outlook. They are
light gray on white which is very difficult if not impossible to read. A reminder is supposed to poop; this color combo is a dud.