Originally posted by -Pr-
I think it's meant to be brown, the colourist just got it wrong.
Brunette characters in comics are often depicted with a reddish hue; it depends on the inker. Lois Lane is a good example.
Here's another pic of Janet w/ reddish hair from back in the old days.
And here's a pic of classic X-men:
(Again, here you see an inker who was probably going for reddish-brown with Hank and Bobby, but he clearly overdid it with the red inks.)
It's pretty common actually.