My son has dark spots in the white of his eyes. They are greyish marks. Is this normal?

Maybe not. Greyish discoloration on the white of the eye may reflect health problems. In some healthy people, grey marks indicate thinning in the white of the eye where blood vessels penetrate (axenfeld loops). People with osteogenesis imperfecta, or other connective tissue disorder, may result in greying of the sclera. Dehydration is also known to cause this. Best to have this checked out by an eyemd.