It appears it's random random, which causes cookbook image diffs every time it's regenerated  https://github.com/ScottPlot/ScottPlot/blob/575117576629a214996d351f4d7a1b16a3877a3a/src/ScottPlot5/ScottPlot5/Plottables/PopulationSymbol.cs#L96