message ColourProtoTest {

    enum Colour {
          BLACK = 0;
          BLUE = 1;
          WHITE = 2;
          GREEN = 3;
          RED = 4;
          YELLOW = 5;
          AQUA = 6;

      }

    // most liked colours; test enums in arrays.
    repeated Colour favourite_colours = 1;

    // why not also test booleans in arrays while we're at it. 
    repeated bool booleantest = 2; 

    // least liked colour
    optional Colour least_liked = 3;
}