Abelian sandpile animation: toppling of an odometer of rational quadratic growth

The odometer is the floor of (3/32)x^2 - (1/32)y^2 + (1/8)xy. This shows the corresponding toppling, on an initially empty plane, moving out in waves from the origin.

[@mistycremo9301]

Admittedly, in short, I'm not certain that I understand what I'm seeing. I'm roughly familiar with the abelian sandpile model, but I'm unfamiliar with the notion of an odometer, and I'm unclear on what this particular color scheme represents