Version: 7.1.3.2 / LibreOffice Community Build ID: 47f78053abe362b9384784d31a6e56f8511eb1c1 CPU threads: 4; OS: Linux 5.4; UI render: default; VCL: gtk3 Locale: en-GB (en_GB.UTF-8); UI: en-GB Calc: threaded Take Draw, for example. Open a Graphic Style in the side bar and change the font colour to white in "Font Effects". Now go to the "Font" tab. RESULT: There is no preview. In Draw, you may, for example, want to use a white text with a black shadow (applied in the "Shadowing" tab) as a "highlight". But the preview still remains invisible. In Writer, you may want a white text against a coloured frame or page, so the question of highlighting in the same Paragraph Style dialog does not arise. And in certain cases you may just want a white font to make it invisible on a standard white page.
Yep, the preview background colour should be adjusted so there is enough contrast according to the chosen font colour. This is more like an enhancement.