No—if the camera recorded the image only in black and white, the original color information was never captured, so it cannot be recovered in GIMP or any other software.

What you can do is create false color for visual effect or easier interpretation. In GIMP, that generally means colorizing or applying a palette/toning effect to the grayscale image. This can make the image look colored, but it will not represent the scene’s real colors.

If you need realistic color, the only option is manual hand-coloring based on outside knowledge of the scene.