Stuart, you're right. The colour values in the rest of the photo look to be pretty accurate. The coin could well be brown! I also agree it looks like a tun mm. Clear on the reverse, but on the obverse possibly been fiddled about with. If an earlier coin had been over struck, why would it be done in such a way? Both obverse and reverse designs and legends completely replaced, but just the tiny area where the mm appears left unchanged? Nah…..