I wasn't able to figure out how to set the attribute for the colors https://observablehq.com/@john-guerra/us-federal-budget-outlays Am I missing something? I couldn't figure it out from the documentation

Tricky! You could use : color: (x) => d3.interpolateRainbow(x * 100) the trouble here is that there are 240 children of the root, and the visible ones are the first ten—with the default interpolateRainbow scheme they all have about the same hue.

Ahhh I see it now, quite confusing imo :)