There is green chalk board paint. I found it in the same brand tin as the black, when I put up chalkboard paint walls in a two of the rooms in the last place I lived. Looked good. A matt dark forest green
I like the under the sea idea too.. I like the connection with being responsible for the sea, when in a bathroom. It all ends up out there. I have reminders of nature and the sea etc in mine.
How to 'join' artistically a chalkboard & disco toilet room with the sea concept however, or does it matter? What I saw immediately was a throne, in a sculpture form around the toilet structure, praps from papermache or plaster of paris and painted gold. This gives me an underwater adventure idea like a dream or a film clip or something, and somehow blends it in in my mind....weird...
What I do like is maybe having the little toilet rooms different. I like one having the websites and contacts of every help organisation avail for whatever thing, eg rape crisis, incest,drug addiction support, abortion counselling, etc etc. In a permanent situation maybe on the back of the door.
One toilet room could have lots of stuff going on like with the info and graffiti and chalk walls and such, and the other...minimalism, zen nothingness perhaps. A clear light colour, maybe in blue with clouds or water spray in white painted on. Or some other contrasting themes.
I like also these two rooms being different as nothing about gender or human sexuality differences but just two different rooms because there are two...why need they be the same.
What if the chalk was in a cool dispenser on the back of the door, like one of those gumball kinda things so that the very action of putting it back was enjoyable...?? Or a cage ball dangling from the ceiling...