Summary
Some color rcParams that can fallback to another rcParam use "auto" to indicate that fallback (lines.markerface/edgecolor, boxplot.flierprops.markerfacecolor, axes.titlecolor, savefig.face/edgecolor), whereas others use "inherit" (legend.face/edgecolor, x/ytick.labelcolor).
There's also legend.labelcolor, which uses "None", but that's a much more complicated case (#28153).
Proposed fix
This should be made consistent. Safest (and not really an issue) would be to just support "auto" and "inherit" with the same meaning for all those rcParams; it would also be possible to pick a single winner, use it consistently, and deprecate usage of the other, although I'm not really sure it's worth the annoyance.
Summary
Some color rcParams that can fallback to another rcParam use "auto" to indicate that fallback (lines.markerface/edgecolor, boxplot.flierprops.markerfacecolor, axes.titlecolor, savefig.face/edgecolor), whereas others use "inherit" (legend.face/edgecolor, x/ytick.labelcolor).
There's also legend.labelcolor, which uses "None", but that's a much more complicated case (#28153).
Proposed fix
This should be made consistent. Safest (and not really an issue) would be to just support "auto" and "inherit" with the same meaning for all those rcParams; it would also be possible to pick a single winner, use it consistently, and deprecate usage of the other, although I'm not really sure it's worth the annoyance.