Titans' Nest

The trick this enchantment pulls is turning your graveyard into a colorless mana battery with a spending clause that reads backwards. Most rituals and ramp fixtures make colored mana; this makes and then forbids you from spending it on the colorless spells usually pays for. The wording ("one or more colors without in its mana cost") aims the output squarely at big multicolored payoffs, not at generic filler or eldrazi. That gap between what the mana looks like and what it can buy is the whole point: it produces colorless, but it only serves colored spells, which makes it an enabler for exactly one class of expensive thing and nothing else. The upkeep surveil feeds the machine, quietly stocking the graveyard with the exact fuel the mana ability wants to exile, so the two halves form a self-contained loop rather than two abilities sharing a card. The cost that balances it is permanent: every exiles a graveyard card for good, so you are trading yard for a discount on something enormous, and the surveil has to keep refilling faster than you drain. That trade only pays in a shell that both fills the graveyard fast and runs a top end worth the sacrifice. Outside that build the enchantment does very little, which is the honest read on a card whose payoff lives entirely in the deck constructed around it.