I've started to try getting from Snow White to Soot Black. Though it's possible I'll stop at a color I REALLY like. I've been using 1 type of fruit until the "feathers" message pops up once, and then waiting. This seems to be a much more stable way to get colors, even if it takes longer. So far:
Snow White + 1 pear (message) = Sylph Green
Sylph Green + 1 berry (message) = Celeste Green
Celeste Green + 1 apple (message) = ?
I'm guessing it'll be a light to mid grey. I'll see in 5 hours.
You just need 1 more plum proc to get snow white.
