Examine source code of Spectrum Grayscale

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Spectrum",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(45, 45, 45)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(30, 30, 30)",
      "tab_background_text": "rgb(212, 212, 212)",
      "toolbar_field": "rgb(37, 37, 38)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(61, 61, 61)",
      "popup": "rgb(37, 37, 38)",
      "popup_text": "rgb(212, 212, 212)",
      "tab_loading": "rgb(61, 61, 61)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4e165ab5-00df-427c-835d-a4271bd28c49}"
    }
  }
}