What color is the triangle at the hoist of Czechia's national flag? Blue. Czechia's flag has a blue triangle at the hoist, extending halfway across the flag, with white above and red below on the fly side. The hoist is the edge attached to the flagpole, so the triangle is the part nearest the pole.
The design began as the red-and-white flag of Bohemia, whose colors closely resembled Poland's flag. To make the new Czechoslovak flag more distinctive, designers added the blue hoist triangle in 1920. The blue element also helped create a recognizable national design without placing a coat of arms at the center.
When Czechoslovakia dissolved in December 1992, the Czech Republic retained the former Czechoslovak flag, while Slovakia adopted a different design. The flag was banned during the Nazi occupation from 1939 to 1945, when a horizontal white-red-blue tricolor was used instead. Its earlier design was restored after the war.