Painter's Palette

At the beginning of each player's upkeep, that
player reveals the top card of their library. Until
end of turn, lands tapped for mana produce
mana of the revealed card's colors instead of any
other color. If a colorless card is revealed, that
player may choose a color.
{2}: Choose a color. Until end of turn, spells cast
this turn are the chosen color in addition. Any
player may activate this ability as a sorcery.