can't add color to photo

I have a bunch of images I downloaded from a site of old documents.  The image are black and white and I have added a little color to each one, but am now at in image which will not allow me to add color.  The Profile for this image is monochrome and unlike the other images, does not give the option for color.  Is there no way to add color to a monochrome image if its profile doesn't reflect that?  Thank you.