Line path effects?

[kdund]

Chiaran O'Hare uses path effects to make a thin black line around lines which helps a lot with seeing lines and lighter colors better
(see https://github.com/cajohare/HowToMakeAPlot/blob/909cda03238a6b772de69e5512059fe25bbeebdb/code/ExclusionLimits.ipynb)

Should we consider using this nice trick?

[yuema137]

Good idea. I will implement it.