Try Plot.normalizeY stroke that follows the fill color, something like: stroke: d => meanAges.get(d.breed) + 2,

That's interesting! One consequence of doing this is that it changes the colors of the fill, since the domain of the color scale expands to accomodate the extra values from the stroke.

indeed, i tried it now :) makes sense BTW i used a similar concept here: https://observablehq.com/@bagami/slucajevi-po-zupanijama COVID trends per county (for Croatia)

Neat! 👍