What color is the "colorful dog"?

What the English call “sticks out like a sore thumb” is called “known as a colorful dog” in German. The linguistic image is different, but the meaning is identical.

Even if you do not deal with the ethymology of this proverb, the question remains what color the colorful dog had: the airmail collectors named a stamp of the “Flugpost am Rhein und Main” (airmail in the Frankfurt area) for the first flight of Ferdinand von Hiddessen on 10 June 1912 overprinted with the name of the aircraft “Gelber Hund” (yellow dog).

The organizers sold these stamps on red airmail cards at three marks, franked with three of these surcharged stamps and a 5 Pfg Germania and guaranteed the flight of this card with the “Yellow Dog”. These cards are called “Red Dog” by some philatelists. 

Now, the organizers had planned to overprint “Yellow Dog” – matching the name – in yellow color, but after printing the first sheet they realized that yellow on orange is not very clearly noticeable and spontaneously changed the overprint color to blue. So the stamp should actually be called “Blue Dog” … the sheet already overprinted with yellow was also overprinted in blue, so that a double print in two colors was created – and these double prints were used like the only one-color blue overprint stamps and sold to the visitors of the air shows in the Rhine-Main area. Of the 100 printed, only 33 double prints have been recovered as of April 2020 – one of which we show here – and will offer in the upcoming June auction.