I was gonna say he looks solid mink to me, I wouldn't say it's a rare colour there seem to be more and more around these days although it's not bred for so not seen as desirable as they can't be shown. I wouldn't pay extra just because he's a solid mink though and also make sure you do the usual checks that he's healthy, his parents are TICA registered (even more important with these uncommon colours to make sure they aren't something like a Tonk or Burmese cross) and his parents have had pkdef and possibly HCM health checks as well.
From what I understand about it a solid mink is a snow version of a melanistic Bengal (black similar to a panther) and it's the mink variant of it.
Also it would be better if you had a side view photo so people could see his rosettes as the colouring otherwise is Tonkinese if there aren't rosettes or spots.
http://www.asuracats.co.uk/coatsandcolo ... ow-bengal/