Vault of Whispers

Black's contribution to the cycle of lands that count as artifacts does two jobs from one permanent: it produces colored mana the way any untapped source does, and it ticks the artifact count that affinity, metalcraft, and every artifact-matters payoff since has cared about. That double duty is the whole design problem, and it is paid for in vulnerability. Naturalize, Shatter, and every Disenchant variant suddenly reach into your mana base, hitting sources that no removal would otherwise touch. Where a basic Swamp answers to land destruction and almost nothing else, this answers to the broad and cheap artifact-removal axis instead, which is the trade the cycle makes for stacking land and artifact onto a single card. The color it produces is the least interesting thing about it: in the environments that wanted it, the question was never whether you needed black but whether you wanted another artifact on the table. That texture (a mana source feeding a removal-vulnerability axis a normal land never touches) is why the cycle keeps reappearing wherever artifact count is a resource worth counting, and why it stays out of decks that just want black mana without painting a target on their manabase.