[hteas]

Nick,
The greens and the blacks are the same stiffness (very) despite the general assumption that they are different. The Grey blades and the ice are softer.
It seems that the makers really don't like to make soft or medium blades. If anything, they go the way of Picasso. Picasso's Start fins have green blades that are as stiff as the black ones. the footpocket is softer to make them easier to kick with.
Omer has their grey and ice blades that are softer, Cressi has the 3000LD, and Imersion has their green fins. Everything else seems to be stiff, stiffer, or unbendable.