Visual suggestion for task graph

The task status has a natural order: waiting -> processing -> memory -> released

The task graph could visually prompt this better:

1) Legend should be presented in that order (top to bottom waiting -> released)
2) Color scheme could better reflect this. Some options:
a) Either a continuous hue with no particular meaning e.g. Viridis4 or Plasma4
b) waiting: gray + traffic lights (processing: red, memory: amber, released: green) (RdYlGn3 / Spectral3)
c) waiting: gray + other three color combos that end in green (https://bokeh.pydata.org/en/latest/docs/reference/palettes.html)

2b is probably my favorite

I think b and c are probably better than a, but the problem with them is that they will break the meaning of the current green changing it from processing to released. But I think it might be worth it because green is the color we are programmed to look for to mean "done" not "in the middle of things". Depending on opinions on APIs though maybe that means a change like that should wait till a big version bump.