A card's color is not verified by the color of their frame. A card's color is determined by their mana cost, by the colored mana there. So, for instance, Kitchen Finks is a green and white creature, affected by cards that affect those. Doran is Black, Green and White. Cruel Ultimatum is a Red, Black and Blue sorcery, so on, so forth. Lands do not have any color because of this, because they don't have a mana cost, so they can't have colored mana in their costs. Since Ancestral Vision does not have a mana cost, it woudln't have a color. But since text always trump rules, it is blue because its text says so. Future sight, for instance, has a red instant that deals damage, which costs 2R , but is colorless, because its text says so.