This one is ON the cliff wall. If you follow the cliff from east to west from 16's gate, and if you go past the jog in the cliff without finding it, turn around again. It's above the mounted Wander, but not super high up.
The problem is that the cliff is not so shadowed that the white tail stands out but also not bright enough to make the dark body obvious. And being up on the wall, the lizard isn't prone to being spooked into running around and getting your attention that way. Playing with the brightness and contrast might make it easier to spot the white tail.
The lizard is on the west side of a slight projection, immediately to the east of the cliff wall with the dark mark on it (which is just before the cliff takes a jog to the north).
Walk a bit east from the dark mark and look east along the cliff wall. You can see a light ridge in the far distance that steps back at the top, a ridge that bulges out higher up in the middle distance, and a dark ridge that angles back in front of that. The lizard is on the dark ridge. (Stand there long enough and it will come down to the ground.)
Alternatively... If you go north from the dark mark and look back at the cliff face, you will see a crevice going up the cliff to the left of it. The lizard is on the cliff face on the left (east) side of this crevice.
Thank you very much man. After I found it thanks to your help I didn't get the trophy... and it was the missing one. I just started a while back a new game+ and went to get all the lizards... now I gotta beat the first 15 colossi to open the gates and get the last three and hopefully get the trophy... wish me luck!
Fench! Currently playing: Modern Warfare 3 MP/Spec Ops, Shadow of the Colossus HD