Nice to see this thread bumped, it's an interesting subject. Well it's 3 years on since my last post and one I'll add is that I actually have a friend, he's a practising shaman, meditates a lot, really balanced individual who knows what he's doing with his life - when me and other friends have tripped with/around him, all of our faces etc will be morphing to oblivion, except his, none of us get any visuals around him.
It didn't make sense to me at first how that could even be possible, that one person didn't produce any visuals at all when everyone else's faces were warping all over the place, but then I thought about how we all knew the guy as being incredibly balanced, stable, etc - and I remembered that just like closed eye visuals, the visuals we see with open eyes are somewhat built up by our thoughts and expectations, so the way we see another persons face when tripping may be related to what we think of them as a person, i.e. if someone has a very chaotic and messy presence, always having problems and conflicts etc then it's likely we may see them in a very crazy/chaotic fashion when tripping, while someone quite balanced like my friend may seem unmoved by the visuals.
That was the best theory I could come up with anyway to explain it. It wouldn't surprise me if I was right though, maybe that's where the whole "Aura reading" fringe stuff comes from - just people projecting their own views of a person on to their vision of them through some kind of synaesthesia they experience.