This issue is related to the call for style overhaul proposals.

My understanding of how line-art markers get drawn (e.g. "x") is that the width of the line reads from the markeredgewidth parameter.

This means that when markeredgewidth is 0, line art markers are invisible. This is particularly a problem for seaborn (where markeredgewidth is 0 by default), but I think one could argue that it is not ideal in any case.

IMO, it would be better to have some differentiation between the width of the edge around a solid marker, which is purely aesthetic, and the weight of the line that is used to draw a line-art marker, which isn't. This distinction already exists a little bit in that line-art markers are colored with the color parameter and not the markeredgecolor parameter (though specifying the latter does appear to override the former). So I would propose one of two things: 1) adding a lines.lineartwidth (or something) parameter to allow separate specification of the line-art marker width, or 2) reading from lines.linewidth instead of lines.markeredgewidth.

A related (but possibly separate; I can make a new issue) point is that it would be nice to have some "hollow" markers, like a hollow "o" or "s" which are really line-art markers with the same basic shape as a circle or square, but without a fill and where the line color is derived from color and not markeredgecolor. It's possible to draw one of these currently, but you have to do something like plt.plot(x, y, "o", markeredgewidth=1, markerfacecolor="none", markeredgecolor="b"). This means it is hard to use this style of marker through an abstract interface (i.e. seaborn), which is a shame because this can be a very useful way to draw scatterplot points.