When you check your notifications, they can come up the wrong color. This is brand new, and it depends on the site. This is on ELU:
Whereas this is on MSE (or SO):
and this is on Mi Yodeya:
It’s also been reported to happen from a cell phone, where some links are red and others blue: "seems random" they said.
So it looks like some of the site overrides are now leaking through the CSS where they never used to.