Paint Roller

Rollers do walls, brushes do blocks. Picking up the wrong one and wondering why nothing changes color is the standard first mistake. You also need paint sitting in your inventory and it burns down as you work, so buy far more than a room looks like it needs.

With Smart Cursor on it stops being a per-tile tool. It spreads out from whatever wall is closest and fills everything connected that is not sitting behind solid blocks, which paints a whole room in one press. That is fast, and it is also how people accidentally recolor half a house.

The Spectre version covers more ground per click and is worth it the moment you paint anything bigger than a single small build. Neither version takes modifiers, so there is nothing to reforge for.