I'd like to achieve the following effect for line markers, as attached. I cannot know in advance the colors as they are configured by the user, and there is multiple lines in the chart. It appears that the trick is to create a border of 2 pixels of the marker, the problem is that the color must be "the line color". And while the marker background inherit the line color, there is no way to retrieve the line color and set it as a background.
Is there a workaround? It would be nice to add a specific keyword for color, so that it basically means "the current chart color".