I'm New- Game Path?

It depends on the program. If you use photoshop, and I assume GIMP would o it as well, you can select different parts of the texture and change the hue and saturation which will keep the shadows intact. Or, if you can find a white versionof the texture to use as a base, you can add your colours on new layers on top and set them to multiply so that the shading below shows through, then flatten your image before you save it.