I also have this problem with kubuntu installation.
There is two possible solutions:
1) change default kde tooltip background color to something light (like light yellow)
2) change libreoffice kde ui to use the correct theme background color. My gtk apps (firefox, chrome) use light blue backgound with black font color.
It seems to be a bug in the libreoffice that does not use the correct pallete color for tooltip font color. The default kubuntu kde tooltip color is white over black.
I also have this problem with kubuntu installation.
There is two possible solutions:
1) change default kde tooltip background color to something light (like light yellow)
2) change libreoffice kde ui to use the correct theme background color. My gtk apps (firefox, chrome) use light blue backgound with black font color.
It seems to be a bug in the libreoffice that does not use the correct pallete color for tooltip font color. The default kubuntu kde tooltip color is white over black.