In settings.json, you can define a settings node named extension.markeditTheming to override colors, for example:

{
  "extension.markeditTheming": {
    "enabledMode": "both",
    "lightTheme": {
      "editor": {
        "textColor": "red"
      }
    },
    "darkTheme": {}
  }
}

• enabledMode: Enabled color scheme (both, light, dark, or none to disable).
• lightTheme: Custom colors used in the light mode, see colors.d.ts for the full spec.
• darkTheme: Custom colors used in the dark mode, see colors.d.ts for the full spec.