Examine source code of light grayscale colors

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "plain light",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(243, 243, 243)",
      "toolbar_text": "rgb(66, 66, 66)",
      "frame": "rgb(222, 225, 227)",
      "tab_background_text": "rgb(140, 143, 146)",
      "toolbar_field": "rgb(255, 255, 255)",
      "toolbar_field_text": "rgb(67, 67, 67)",
      "tab_line": "rgba(248, 112, 140, 0)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(65, 65, 65)",
      "tab_loading": "rgba(248, 112, 140, 0)"
    }
  }
}