Contours not coloring correctly

[Plantain]

I am trying to draw contours, but the contours are not getting colored according to the specified domain. My expectation is that if I clamp the domain to the threshold range, that I would get the full range of colors used in the contouring, but that seems to not be the case for reasons I do not understand.

https://observablehq.com/d/79ecd1f124a6ec5e

I also do not understand the significance of Plot.identity from the docs (https://observablehq.com/plot/marks/contour) or understand when and how it should be used. It seems to just produce blank charts.

[Fil]

Plot.identity would color with the datum, which is an object {time, altitude, ti}. I think you want fill: "ti" instead. I'd also recommend to use x: {type: "utc"} (or x: {type: "time"}) for a more readable axis.

[Plantain]

Thanks!