UK, 1962—a type of pedestrian crossing distinguished by black-and-white chevrons marked on the road, and having traffic warning lights activated by people wishing to cross—alludes to the black-and-white fur of the giant panda
Australia, 1944—jocular—denotes the Yarra River, which flows through Melbourne, Victoria—alludes to the brownish colour of this river, the image being that the mud is on the top, not at the bottom, of this river
UK, 19th century—‘red on the map’: the colonies and dominions of the British Empire—‘to paint the map red’: to expand the territory of the British Empire—from the colour used to represent British colonies and dominions on maps
Australia, 1950—a traffic warden in the state of New South Wales—‘brown’ probably refers to the colour of those traffic wardens’ uniform—‘bomber’ may refer to the fact that many of those traffic wardens were originally war veterans; or perhaps to the Australian-English use of the noun ‘bomb’ for an old car
military slang, 1944—a medal awarded to all members of a force—especially the 1939-1945 Star, awarded to British service personnel who took part in WWII—refers to the ubiquitousness of Spam as a foodstuff
Australia, 1970—a Melbourne City Council parking officer—the adjective ‘grey’ refers to the colour of those officers’ uniform; the noun ‘meanie’ refers to the nastiness displayed by those officers in the accomplishment of their duties
USA—‘blue-sky talk’ 1900—‘blue-sky research’ 1947—the adjective ‘blue-sky’ is used to mean: (in negative sense) fanciful, hypothetical; (in positive sense) creative or visionary—from the notion of a blue sky as a place free from disturbances or difficulties
Australia, 1865—to be less of a fool than one appears to be—this phrase plays on two uses of the adjective ‘green’: 1) denoting the colour of growing vegetation, grass, etc. 2) denoting an inexperienced or naive person
‘red rag’—a piece of red cloth used to provoke an animal—hence, figuratively, a source of provocation or annoyance, something which excites violent indignation—the notion occurs in the late 16th century