Peoples' voices sound different, I tend to think in a more abstract manner some times, music sounds better, I'm relaxed (depending on where I'm at), and my stresses flow away. I feel as if I'm being cleansed, or after I'm done with energy work/rituals, I feel very calm and peaceful.
I can sense other peoples' vibes more easily after sparking it up, and it's easier to commune with the spirits/god/goddess. As far as seeing funny colors, that happens after I close my eyes. Nobody would be none the wiser if they saw a blind person smoking a joint, most of the time. I see it as a gift from the Gods, and I treat it as such.