I don't honestly know. Usually the complex greens are pretty neutral in terms of color contribution, I think. I've only done a few crosses along these lines myself. I know that green x white = white (usually). What I'm thinking is that the color of King Arthur is pretty darn nice, size is pretty good, and it is really the form that is lacking if you compare it to modern breeding.
I have two options that I'm seriously considering (based on what is blooming right now). One is Paph. Freckles 'Moonstone' (a beautiful almost perfectly formed little thing, unlike most of the Freckles - but smallish). The other is a Paph. Primcolor (primulinum x concolor), which again is small but amost perfectly round and armeniacum yellow (another oddity, most Primcolors aren't round). Since I have lots of divisions of King Arthur in bloom, I could try a few different things, I guess.