Umm, yeah, I expected such things but forgot about that particular bug.
FWIW: We now have the native color that we were trying to hardcode and we should use it unless the native color is broken somehow. Making a native color slightly darker doesn't seem like a proper use case for windows-default-theme. See bug 426660 comment 25. See also bug 431666 comment 5.
Umm, yeah, I expected such things but forgot about that particular bug.
FWIW: We now have the native color that we were trying to hardcode and we should use it unless the native color is broken somehow. Making a native color slightly darker doesn't seem like a proper use case for windows- default- theme. See bug 426660 comment 25. See also bug 431666 comment 5.