18 percent grey
I’ve painted my gallery wall a light/mid grey (it says Turtle Dove on the tin, I couldn’t get Battleship). The old wall was magnolia which is fairly bland; not white but not a shade of anything really. The wall needed patching having removed one shelf and then moved another, so I took the opportunity to change the colour to somethimg which I think shows off my work better, especially with white frames. It also photographs much better, the magnolia either looked off-white, or if I tried to brighten the image afterwards, it was a balancing act between getting the wall to look less creamy and over-exposing the artwork.
It wasn’t until just now that I made the grey connection with the traditional way of metering in the black and white zone system. A grey card was used to calibrate the film exposure. The mid grey used reflects 18% of the light hitting it hence the term 18 percent grey. Getting far too technical I know, lots more here if you’re interested.