Guernsey Blue

The pillar boxes on Guernsey are a distinctive blue.

In Googling around this subject, I turned up a querky fact. There was a period on the mainland when blue boxes were briefly in vogue between 1930 and 1938 for air mail letters only. After this, it was deemed too costly to have separate boxes for air mail and ordinary mail. Just one such blue box now exists and that's outside Windsor Castle, where it stands as a tourist attraction only.