How significant will the White Sand be to the cosmere? Any hints on the Shard that resides there?
Moderately. (Its magic has some cool ramifications for off world use, and several characters factor prominently into the Cosmere.)
Is there more than one magic system in white sand?
Only one in the current outline.
Does the one magic have more than one variation? Because I got the impression that there was something going on on the Darkside? Though I guess the Sky Colors (I think that's what they're called, I read the draft you send out early 2014 so my recollection is a little fuzzy) don't have to be related to magic. Or you could have written them out if they were...
In intended the colors on Darkside to be more a matter of the ecology than the magic--though, on that planet, magic and ecology are very closely tied together. (Well, I guess most of the magics are.)