I can select the head mesh and weight paint without problems. Other objects the rig controls like shirt are not showing in weight paint - they are staying grey. In weight paint face masking they are showing as Green. In vertex select they can be seen and changed. In weight paint vertex mask no vertex is visible and only the Green surface is shown.
I can manipulate and modify the weights of the other objects but only the Head is shown in weight paint mode. I hope this is something silly I am overlooking because it has left me very confused. Any ideas?