VS Code documents color customizations for tabs in the theme color api.
To edit the tab colors you can use the following identifiers:
{
"workbench.colorCustomizations": {
"tab.activeBackground": "#ff0000",
"tab.inactiveBackground": "#ff0000"
}
}
You add that to your settings.json file

To change the tabs header you can use the following:
"workbench.colorCustomizations": {
"editorGroupHeader.tabsBackground": "#ff0000",
}

You can type tab. and it will suggest similar properties you can change