That's an interesting observation. I never saw that with my bigger groups. My nested pair at Dallas didn't have color at all... full silver. (Actually all of that group were full silver with dark grey tails.)
My solo arapaima at Underwater Adventures in MN was almost 1/3 bright red from the tail up once she hit 6' long.
My solo arapaima at Underwater Adventures in MN was almost 1/3 bright red from the tail up once she hit 6' long.