In the Insiders' Build and likely in the February 2020 release is the ability to separately color the veritcal rulers. See https://github.com/microsoft/vscode/issues/54312 - Support multiple rulers with different colors. Usage (in settings.json):
"editor.rulers": [ { "column": 80, "color": "#ff00FF" }, 100, // <- a ruler in the default color or as customized at column 0 { "column": 120, "color": "#ff0000" }, ],