This bug was introduced in #192 and only affects signal plots using the colorByDensity argument.
This code should produce non-overlapping graphs, but currently it does not:
Color[] colors = new Color[]
{
ColorTranslator.FromHtml("#73D055"),
ColorTranslator.FromHtml("#1F968B"),
ColorTranslator.FromHtml("#39568C"),
ColorTranslator.FromHtml("#440154")
};
plt.PlotSignal(data, color: Color.Red);
plt.PlotSignal(data, yOffset: -40, colorByDensity: colors);