Kind of brown/auburnish... I actually preferred her hair that way as opposed to the jet black hair. Helped her stand out more when juxtaposed with Superman/Clark Kent.
Yeah, in comics (and real life as well), characters with brown hair often have a reddish hair undertone of sorts. The intent isn't to make them true redheads (just lighter brunettes), but, because of the inks used, red is what people see in the finished product.
Here are some good examples:
We all know that Bobby Drake and Hank McCoy aren't redheads (they have brown hair), but because of the inks used in this particular image, it almost appears that way.
Now, look at this picture, which is meant to reflect the same time period in which the events depicted in the previous image took place. Here the colorist used slightly different shades of brown for Hank, Scott and Bobby without making either one of them look like a redhead. Job well done.
Another brunette character, Janet Van Dyne, sometimes appears to be a redhead when inkers apply the same technique.
Janet as a brunette:
Janet appearing as a redhead because inks were overdone:
It even happens with eye colors!
Here, we have an inker trying to give Lara Croft
slightly lighter brown eyes. Oddly enough, the character ended up looking like she has dark red eyes!
A similar technique is also used with black hair and blue inks. In this particular image, it looks as if Superman's hair color is almost entirely blue! Obviously, Superman's hair is jet black though.
Anyway, that's just something I've observed over the years. Carry on. lol