Colorless Eldrazi spells you cast costless to cast.
, : Search your library for a colorless creature card, reveal it, and put it into your hand. Then shuffle your library.
3/1/2010 Eye of Ugin doesn’t have a mana ability.
3/1/2010 Eye of Ugin’s second ability lets you find any colorless creature card in your deck, such as an artifact creature card that has no colored mana symbols in its mana cost, or a creature card that’s become colorless due to Mycosynth Lattice.
4/15/2013 Mistform Ultimus and creatures with changeling are Eldrazi. If they become colorless, possibly due to Mycosynth Lattice, Eye of Ugin would reduce the cost to cast them by .