The triangle at the hoist of the Czech Republic’s flag is blue. It extends from the flagpole side halfway toward the fly, separating the white upper band from the red lower band.
The flag’s design originated with Czechoslovakia. After independence in 1918, the new state initially used Bohemia’s white-and-red banner, but it looked too similar to Poland’s flag. A blue triangle was therefore added at the hoist, and the design was officially approved on March 30, 1920.
The flag was banned during the German occupation from 1939 to 1945, when a horizontal white-red-blue tricolour was used instead. After the Second World War, the earlier design returned. When Czechoslovakia dissolved in 1992, the Czech Republic retained the historic flag while Slovakia adopted a different one.
The blue section is sometimes mistaken for a chevron, but it is formally an isosceles triangle. Another frequent error is drawing it too short: its point should reach the midpoint of the flag’s length.