windows dark theme and office colors
This issue occurs with Windows dark themes, or when the Window color in Control Panel\Appearance and Personalization\Personalization\Window Color and Appearance\Advanced appearance settings... is set to a non-white color.
In this situation, any gray scale color in any Office program (Word, Excel, Powerpoint) is changed. Applying 'white' to an item actually applies the window color defined above.
As highlighted in https://answers.microsoft.com/en-us/msoffice/forum/msoffice_excel-mso_windows8/excel-and-high-contrast-theme-non-workable/753ecdcb-08e1-4396-b0df-4854cdb06f05, this is unworkable for several reasons.
I'll add my own experience here with Powerpoint:
1/ I want a presentation with a white background. So I have to set the background color to ... black (very intuitive, isn't it?) !!! If I run the presentation from my computer, that works ok. But if I send the presentation to somebody else, what does he see ? A black background presentation. Basically from one computer to another the presentation itself has to be modified to show up properly.
2/ I'm creating a new presentation based on the built-in themes. The normally white background is black. I have to switch the color (to black !!!) every normally white item so that it appears ... white !!!
In essence, the color palette inside Microsoft Office should not be modified (especially in such a counter-intuitive way) by the UI settings of the machine where a document is opened. At the very least, it should be possible to disable this 'feature' in MS Office.
I had to switch to using exclusively LibreOffice because of that issue. In LibreOffice, the document background does not depend on the Windows color scheme of the machine you're working on. As it can be expected.
Thanks for looking into this issue (and fixing it as soon as possible).