For the Devs: a request from a fan

The inability to paint doors is likely related to their behavior. The fact that they animate and have an open and closed state means they’re not implemented the same way as regular, paintable blocks. For the closest thing to a ‘secret’ door, I would look into the false wall shape. It’s a weak, two block high sheet that’s flush with other blocks, that the devs use for monster closets. You could place and paint this shape so as to hide an entrance. The downsides would be that it has no strength, and you’d have to replace it every time you use it.