These are eight small empty buildings with different ground textures, which can be used as terrain paint in game. They require no resources or build time so they can be placed instantly, and do nothing except change the terrain texture.
When demolished they will leave the same texture behind that they have when you place them (I recommend to demolish them right away, since who knows what routing issues may arise from having a bazillion empty buildings in game).
They are in their own group in the Decorative section, with custom icons. The group icon is that of the furnace (which totally looks like a paint bucket to me). Note that when you use the default user interface, all icons have an orange colour overlay — it’s the game that does that, the actual icons look normal.