I dunno... in my first grade, many years ago, we had reading groups divided into Green Light, Blue Light, and Red Light according to how fast we were learning. No one thought too much about it at the time.
Similarly, except I remember random bird names. Blue Birds, Cardinals, and Robins, something like that. The kids knew which was the smart group, which was the middle, and which was the slow. At least those of us in the smart group did . . .
I was in the Chickadees reading group in third grade; the highest rank in the class. I thought it was cool.