in vscodium I have a different left bar color for each project - not exactly what you want but I can easily differentiate between them.
There is a workspace settings json file per project:
"settings": {
"workbench.colorCustomizations": {
"activityBar.background": "#faf7c7",
"activityBar.foreground": "#000000" }
}
(disclaimer: this works on Debian Gnome)