Solution that would be nice its additional field "crosshairMarkerColor" to addLineSeries settings

const lineSeries = chart.addLineSeries({
    crosshairMarkerVisible: true,
    crosshairMarkerRadius: 6,
    crosshairMarkerColor: '#111',
});

Today I was checking out the library and MSVC warns for https://github.com/alandefreitas/matplotplusplus/blob/359a775710e1b1fd5667281a0855806f149b7ab0/source/matplot/util/contourc.cpp#L1771

BOUNDARY_S returns a bool do the expression is bool > 0