Reproduction instructions:

1. In Calc, navigate to Tools > Options > LibreOffice > Appearance
2. Choose the Dark theme (and ensure no other UI customizations).
3. Enter some data.
4. Create a Column-type chart using your data
5. Make sure there are labels, e.g. a Legend and Axis labels
6. Leave the Chart area by double-clicking outside of it.
7. (Possibly) resize the chart

Expected results:
Chart labels appear in White, or nearly-white, color over the dark background, both when the Chart window is active and when outside of it, in Calc.

Actual results:
When leaving the Chart for Calc, sometimes the label text becomes black; at other times, the labels don't turn black, but resizing the chart makes them black.

Build info:

Version: 26.2.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: 7ef1c437f30b0869a5b9fa33809bac2c6665ace3
CPU threads: 4; OS: Linux 6.12; UI render: default; VCL: gtk3
Locale: en-IL (en_IL); UI: en-US
Calc: CL threaded