After looking at it again, it may be sorting by rarity then color, with commons showing up first sorted by color, then uncommons sorted by color, then rares sorted by color. As I was noticing 'chunks' of a color within a set, but not a complete color sort. If it sorted by color, then alphabetical that would be fine also, but as it is, it makes it a bit odd looking at a visual spoiler.
This rarity sort becomes more obvious when looking at it in list view. I often use the spoiler mode view. It would be easier for me to skim over the set looking for a card that way than it would be to remember what rarity it was printed at. It would make the visual spoiler mode more logical to me as I'm browsing. In fact it would just be nice to be able to define the secondary sort.