I have tried to change font colour to red in cells but colour stays as black. I imported spreadsheet from Excel. There may be some hidden formatting as I did not write the original spreadsheet
My very first idea - Conditional Formats. If your original file has conditional formats defined and active, then any format changes won’t get effective until conditions are met no longer.
Second idea - since you noticed that the file is from Excel, it may have been opened “read-only” and thus you may not be able to change anything.
The sheet has rows of alternating white and pinky background, I seems to be on the pinky background that stays black.
Ok - then please check Format → Conditional → Manage for conditional formatting or provide a anonymized sample file.
A bit late maybe, but I faced the same issue.
Sorry for necroposting!
I solved it unchecking View/Value Highlighting (or toggle with Ctrl+F8)