Brunette in the 1960s films

1968 b/w series still implies dark hair by the way she's colored

Sandy blonde in the '79 series

Light brown hair in 1980 film

Back to blonde in 2001, but her eyes turn green.

Orange hair in RE: film (2012), and her eyes remain green.

Ishinomori had her as a blonde (except in some colorspreads)

And the Archaia series seems to vary between having her hair be dark blonde or orange. Maybe she's a strawberry blonde.