In v1.43 is the ability to separately color the vertical rulers.
See issue Support multiple rulers with different colors - (in settings.json):
"editor.rulers": [ { "column": 80, "color": "#ff00FF" }, 100, // <- a ruler in the default color or as customized (with "editorRuler.foreground") at column 100 { "column": 120, "color": "#ff0000" }, ],