I suppose when one wears as many hats as Queen Elizabeth has worn over the course of her lifetime, ordering a preferred style in a few colours just makes sense. In the mid 1970s, she wore versions of the same hat with high, upfolded bumper brim trimmed with silk lily-of-the-valley flowers, in three distinct colours :
Look #2: Green worn during Silver Jubilee visits to Papua New Guinea and New Zealand, both in February 1977. This hat’s crown and brim are both made of fine straw and the hat is trimmed with a straw bow, low on the back of the hat.
Look #3: Blue worn on Silver Jubilee visits to Australia in March 7, 1977 and Northern Ireland in August 11, 1977 and on a state visit to Qatar in February 22, 1979. This design seems to be a carbon copy of Look #2 in terms of material and trim but in this lovely shade of blue.
Photo from Getty as indicated