Indigo Faerie

The activated ability is a color-fixing weapon pointed in an odd direction: not at your own mana, but at the board. For one blue mana you can paint any permanent blue, and the value lives entirely in what cares about that color. Blue-matters effects (the ones that count blue permanents, or that gate a benefit behind controlling something blue) get fed a target they never had. Anything keyed to attacking or blocking a specific color, any pump tied to "blue creatures you control," any drawback that triggers off color, can be reshaped one permanent at a time. The catch is that it stacks color rather than replacing it: a permanent becomes blue in addition to its other colors, so this never strips a creature out of a protection-from-blue shell or fixes a devotion problem by subtraction. It only ever adds. That narrows the card to enabler duty for builds explicitly organized around the color blue itself, and the body it rides on, a 1/1 flier, is the chassis those builds were going to want anyway: an evasive one-power creature that holds its activator open. It is a niche the design space rarely revisits, because most cards that care about color care about a creature's color at a fixed moment rather than one you can grant at instant speed and take away again at end of turn.