Command Tower is the classic example: Its colorless from a deckbuilding standpoint because it doesnt have colored mana symbols printed on it, but it still fixes you perfectly in-game because it only makes colors your commander actually has
Say hello to the new Craterhoof Behemoth
Shroud is a bit of a double-edged sword, however, as you can no longer target your own artifacts with spells or abilities either, but more often than not the trade-off is well worth it
So there we have it, spend enough mana in a turn and you give one of your creatures trample and +1/+1, as well as triggering their valiant ability if they have one
It's important to note that prices will fluctuate over time
Foils carry less risk of reprints, especially if Wizards does another batch of Challenger decks which theyve indicated they will do