Some of this new colored doors have a peephole, in which you can see the door is a 3D model (because of the depth you see on that peephole); you can't see the voxels.

This happens with the old normal door (Oak door) and the iron door, but just when you're holding it in your hand. When you place it, it looks flat, as it doesn't had any peepholes. This model is inconsistent with the new ones.