After double clicking a cell for editing in Calc the font changes to a difficult to read yellow. How can I change that colour? The font colour seems to have changed with a recent update [LO 6.2.5.2.]
Did you try to reset you user profile? The only thing I could imagine to make this behaviour happen, is a Calc default template containing a “yellow” font color under Font Effects (no LO version has been delivered using this color in a default template).
To make a test whether this is coded into your profile, restart LibreOffice in Safe Mode using Help -> Restart in Safe Mode and select button Continue in SafeMode. Open a Calc and test. If the observation is gone, then you have the color defined in a default template within your user profile.
I can’t see that behavior, please test Menu/Help/Restart in Safe Mode.
Same problem in safe mode and after user profile reset. Screenshot is here
Maybe some option about accessibility like Menu/Tools/Options/LibreOffice/Accessibility - Options for high contrast.