cannot implicitly convert enum class to numeric

color.cc

enum class Color {
  Red, Green, Blue
};

Color color = Color::Red;
switch (color) {
  case 0: // error: could not convert '0' from 'int' to 'Color'
    break;
  case Color::Green:
    break;
  case Color::Blue:
    break;
}


if (color) { // error: could not convert 'r' from 'Color' to 'bool'
  // ...
}