How to set the color of inactive tab on the tab bar?

[ZYinMD]

As shown below, the 3rd tab is focused, its color is set to equal the color of the shell, which is nice, but the inactive tabs are too similar to make the active tab stand out:

[ZYinMD]

2 months later I found the answer:

{
  "theme": "foo",
  "themes": [
    {
      "name": "foo",
      "window": {
        "applicationTheme": "dark"
      },
      "tab": {
        "background": "terminalBackground",
        "unfocusedBackground": "#fff"
      }
    }
  ]
}

The unfocusedBackground is the value that matters. The key point is to create a new theme name of your own, foo in the example above.

Doc: https://learn.microsoft.com/en-us/windows/terminal/custom-terminal-gallery/theme-gallery