colorization – Colorize orthochromatic print with Gimp

I’ve just started working with Gimp, and I would eventually like to try my hand at colorization. One photo I would like to do is of my father and mother from circa 1943. He is in his uniform, and his unit patch (63rd Infantry, “Blood and Flame”) can be seen. However, it appears that the picture was taken on orthochromatic film, because what would be red shows up as a deep black. The same is true for the lipstick my mother is wearing. How can I make these appear as appropriate shades of red? Simply adding a red layer doesn’t work, since it is swallowed up by the black.