Many lands have some sort of light color treatment in the frame to remind you what colors of mana they can produce, but this doesn't give them a color. A card's color is defined by its mana cost and color indicator, plus effects from other cards that are specifically changing its color somehow. By itself, Seat of the Synod doesn't have any of these things, so it's colorless. Pyroblast won't do anything to it.
March 14, 2016 11:50 a.m.
Thank you Rhadamanthus. During the game we considered this, but were unsure about it.