The whole thing is about the texture made with inkscape, so you can make the economy of ten minutes :) Can be useful to keep track of your lighting setup. Or to drop as an accessory in a scene. This tool comes from photography : https://en.wikipedia.org/wiki/ColorChecker
You're welcome :) (I should update the file, the normals are inverted I believe...)
I was wondering if I could use the photo when I saw it (where the rabbit is ^^). By the way thanks for all the WDR stuff.