i have the beige/brown viton tubing, so it's difficult to directly compare its appearance with the black, but the viton does appear to be more matte than the santoprene (tho the difference is less noticeable than it was going from epdm to santoprene). the viton is definitely denser/heavier though, and as a result, when you run the two alongside each other and incrementally bend them, the viton doesn't collapse until deeper into the bend.
and i had a (crappy) pic of the epdm in my build in a similar setup to how i have it now with the santoprene, so figured i'd try and mimic the shot so you can see somewhat of a comparison. left is mcmaster-carr epdm, middle is santoprene only, right is santoprene + viton ("beige" color) just kind of laid in there. please ignore the dust ?