Paintbrush

The brush is only half the tool. It needs paint sitting in your inventory the way a bow needs arrows, and it burns a can per tile it colors, so a large build eats through dye faster than most people expect. Buy in bulk before you start rather than partway through, because running dry in the middle of a wall leaves a seam you will see forever.

The base reach is short enough that painting a tall structure means climbing it one platform at a time. The Spectre version extends that reach and is worth building the moment you can, since the scaffolding it saves you outweighs the bars it costs. Neither version accepts a reforge, so there is no prefix to chase and no reason to visit the Goblin Tinkerer with it.