Apply a dye to this, then swing it at structures to paint them.
— In-game Description

The Paintbrush is a decoration tool that allows for the painting of structures with dyes.

The Paintbrush can be used to color your placed buildings by applying the dye to the Paintbrush, then equipping it and using it on the desired buildings. Some parts have multiple dyeable areas, making it possible to have different colors on the same building piece.

Once a dye is applied it is good for a limited amount of uses before the Paintbrush no longer has any paint on it, requiring another dye to be used.