The category Schematic text & graphics matches the color, and in the top-right, Override individual item colors applies.
Override individual item colors can be deselected and then applied with OK, but it reverts immediately to selected, likely because this is a part of the wDark theme.
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Why does this behavior only apply to arcs and not lines?
Is there a means, with the theme still applied, to manually color arcs and other shapes?
Preferences > Colors > New Theme > name your new theme then OK will give you a new theme that is both able to be modified AND will start with the theme you are already using.
ie. It will give you a modifiable version of “wDark”.