I did put a lockable
door on. It opens fine from inside when locked from the outside. I do not think you could paint them. My are next to white split face block, so they look OK. And yes, they are expensive.
On the
lock, I may take those off this year, because when it gets really cold it freezes. This makes it very hard to open. It is only occassionally, but I would rather be safe than sorry.