Thanks a lot for the help! There must be some misunderstanding on my part, but I don’t understand why the higher end of the color scale (darkest blue) does not align with the maximum in my data. I would have thought that I could at least use the domain for the color channel to control this. Which is the way it works here: Scales | Observable Plot
Setting type: “log” in the color channel gives something usable, so I going with that now.
I think the misunderstanding is on me: I thought the domain was both negative and positive numbers, with different orders of magnitude. If they are all the same sign, a diverging scale can work but needs to be given a pivot (which will then correspond to the center color, say the yellow in RdYlBu). (You can also use a diverging color scheme (such as RdYlBu) with a logarithmic scale.)