A Christian blogger has warned that mandalas in adult colouring in books could be dangerous. She suggests that the magical new age claims made about mandalas are true, that they have the ability to heal if you meditate on them and that a good way to do this is to colour them in. Of course, as these magical claims are not Christian, they must be bad and Christians should stay away from them.
This is a view I see echoed by a minority of Christians, who seem to believe uncritically that all supernatural claims are true (e.g. ghosts, crystal healing, etc), but that they come from the devil as they are not specifically Christian ideas. I think the better stance would be to just say that they are not real, but I wonder if that's hard to do when you already hold a belief that is not supported by good evidence.