'Blue Boot' was a British unrealised deception plan by the Twenty (Double X) Committee to 'leak' to the Germans that in the event of a German landing, British troops were to adopt a special distinguishing mark to differentiate them from German troops in British uniform (January 1941).

One of the proposed distinguishing features was blue paint, which was to be used on the right boot, and whose appearance on or behind an invasion battlefield would indicate that the wearer was in fact a German.