Using dark mode in writer via option → Application Color → Scheme → LibreOffice Dark. The inserted formula and its border are still black, so it becomes barely visible in this dark mode. I can change the formula border color by setting the Object boundaries in Custom Colors menu. But how to change the formula text color?
LibreOffice 7.3.2.2 on Arch Linux
Please make your question easy to understand to people who are peeping over your shoulder.
By “formula”, do you mean some sort of mathematical formula created by Math and inserted into a Writer document? Or is it a formula in a table cell?
Don’t forget to mention your OS name and LO version.
The formula from Insert → Object → Formula Object. LibreOffice 7.3.2.2 on Arch Linux
Remember that a Math formula is created outside Writer in an independent application (which in addition does not evolve at the same pace as the others). Once created, the formula object is handed over as a “frozen” one to Writer, just like an image, and won’t react in any way to UI customisation.
You didn’t tell why you chose the dark theme. If you intend to use the resulting document on screen (as a kind of presentation), you can play with the colours in Math so that the overall appearance matches Writer. But, if the document ends up printed, the simplest approach to avoid complicated management issue is to set your UI in Writer to look like a sheet of paper, i.e. a white background.
And if your document is effectively a presentation, build it with Impress which is specifically designed for the task.
tdf#148505