I have found a way of turning a greyscale in to RGB. There is probably a proper way to do it, but this works for me.

Open a blank page. FILE > NEW > RGB > choose the appropriate dpi and height x width. Drag and drop your greyscale image and you now have a photo that be coloured or sepia toned.

Sally

What is the difference if one were to just change the image "mode" to RGB?