The flag is composed by 2 colors, blue yellow in the Nordic cross. The actual design was adopted in 22 June at 1906, but the project was dated by 1521.

These two colors were predominant in Swedish’s arms first time in 1442, right before the flag was idealized and some decades after Sweden becomes a Christian country.

The Nordic Cross represents Christianity.

Curiosity: There’s a rumor, that says that the colors of an argentine football team called Boca Juniors(who had the unlucky fate of facing Corinthians at Libertadores Cup) are blue and yellow because that the colors of their flag will be the same as the first the ship that arrived in the port of Buenos Aires.

Sweden's flag.

Boca Junior's football team flag, same collors as the Sweden's flag.