@BugDevil "All recent artworks I've seen had a far darker shade than the one from the original hair color."
I take it you're talking about fanart. Some people probably thought her hair color changed just like you and started drawing her like that. They're wrong though.
"I'm just saying, seems like a course correction to me."
And I'm saying you're wrong. If that was the case the cover for the novel would have been changed too. The novel is her canon color after all.
"And it doesn't affect Sayaka's hair at all?"
It did affect Sayaka's hair too. It's clearly darker and more red-ish looking than her real hair color. Just compare the cover for novel 3 which shows canon colors for both Sayaka and Haru to that picture. The difference is clear for both Haru AND Sayaka.