26 is pretty close to 30, I have the same issue, but not only with tabs, the fonts are brighter, too! Strange win32 has no comment.
In all, the "The authentic look" has a very close, proper colour representation to what I'd expect.
https://github.com/win32ss/supermium/issues/627#issuecomment-2132659118
I have the issue on XP, too.