metamask-extension/ui/css/utilities/colors.scss

:root {
  // Accents
  // Everything below this line is part of the new color system
  --mainnet: #29b6af;
  --ropsten: #ff4a8d;
  --kovan: #9064ff;
  --rinkeby: #f6c343;
  --goerli: #3099f2;
  --localhost: #29b6af;
  --flask-purple: #8b45b6;

  // DO NOT CHANGE
  // Required for the QR reader to work properly
  --qr-code-white-background: '#fff';
}