I love this idea. I would do it, get removable wall paper. - "A neighbour of mine has one wall in their house papered like this. Every time a new guest comes in, they are asked to colour-in a character and initial it.
♥ jmk says:- DIY Color In Wallpaper is covered in Burgerman monsters (conceived of by Jon Burgerman who is one of the UK’s foremost illustrators). The print is ready and waiting to be colored in by kids (and let's be honest - adults too). The artwork is printed on thick, heavy weight wallpaper and can be colored on using markers, pens, or paint.