If you wanted to colorize in gimp ... first, as Nightvision_UK mentioned, convert it to grayscale. Then add transparent layers on top, set mode to overlay on the transparent layers, play with your opacity, and color on the transparent layer. I would add many Trans layers to separate the color scheme desired so the layer's opacities don't conflict. --- this is a basic way of getting started colorizing photos.

Suite of gimp plugins for texture synthesis. Contribute to bootchk/resynthesizer development by creating an account on GitHub.