A: I don't know I have them mounted on ceilings that are white. I would think you can paint them though
A: Yes with semi gloss paint or egg shell
A: When you need to open the panel, gently insert a flat blade screwdriver into one of the small slots located near the corner of the inner cover. this releases the inner access door and separates it from the outer ring. It is held in place with friction from a plastic tab. To close the door re-seat the inner panel into the outer ring and "snap" it back into place. Friction of the snug fit holds the door closed.
A: Flat head screw driver.
A: I used DAP kwik seal adhesive caulk - white. Be sure to use plenty of caulking as it will shrink as it dries.
A: I used liquid nails.
A: It does open but I’m unsure if the door is removable.
A: Less than 1”. It is flexible too so you could even bow it to remove it without opening it at the hinge at all. Just bow it and pop it out. We used it for chimney clean-out access in finished wall in basement