The yellow/blue cube in f102v2

[Koen G]

Those soapberries are awesome, I had no idea such a thing existed. 

I must say that some images of "traditional soap"  do remind me of this cube:


(I have no idea what the above soap is made of and how, but the coloration pattern is similar.)

However, this does not solve the blue problem. Interestingly, when I asked google how to make blue natural soap it told me to use indigo powder