How to change indent guide line color between brackets in VS Code?

Update for vscode v1.81 (in Insiders now and presumably in Stable early August 2023):

These colorCustomizations have been added so that you can separately color the first 6 indent guides – counting from far left in your code to the right, see the demo):

  "workbench.colorCustomizations": {

    "editorIndentGuide.activeBackground1": "#ffc400",
    "editorIndentGuide.activeBackground2": "#ff0000",
    "editorIndentGuide.activeBackground3": "#a51283",
    "editorIndentGuide.activeBackground4": "#ff8c00",
    "editorIndentGuide.activeBackground5": "#ffc400",
    "editorIndentGuide.activeBackground6": "#ffc400",

           // non-active indent guide colors
    "editorIndentGuide.background1": "#0066ff",
    "editorIndentGuide.background2": "#00e5ff",
    "editorIndentGuide.background3": "#00e5ff",
    "editorIndentGuide.background4": "#00e5ff",
    "editorIndentGuide.background5": "#00e5ff",
    "editorIndentGuide.background6": "#00e5ff"
  }

Notice that editorIndentGuide.activeBackground1 and editorIndentGuide.background1 refer to the indent guides on the far left and so on. Only one activeBackground is colored at a time – at whichever level it happens to be from the left.

VSCode v.1.23 (released May, 2018) added the ability to colorize the active and other inactive indent guides:

"workbench.colorCustomizations": {
    "editorIndentGuide.activeBackground": "#ff0000",
    "editorIndentGuide.background": "#ff00ff"
}

See release notes indent guides

If you only want the active guides to be visible, set the background of the inactives to transparent ala:

"workbench.colorCustomizations": {
    "editorIndentGuide.background": "#fff0"
}