Why are some World Cup team jersey colors different from their national flags?
Italy:

It is no secret that the color of the Italian football team is blue, which is often worn with white shorts, while Italy’s flag consists of three colors; green, white and red.
The mystery behind the blue jersey dates back to the reign of the monarchy in Italy from 1861 to 1946, during which time the Italian Football Federation was established, which in turn decided to adopt the color of the royal family of Savoy, which is blue.
The Netherlands:

The orange color of the Dutch team and its fans dates back to six centuries ago, specifically during the 16th century when the Netherlands led a revolt against Spanish rule in search of independence.
During the 80-year war, Prince William III of England, known as William Orange was one of the most prominent leaders who helped liberate the Netherlands. After independence, the Dutch rebel group decided to adopt the color orange in the flag in honor of Prince William who was appointed governor of the Netherlands in 1555
Germany:

According to the book entitled “All the Colors of Football” by Sergio Salvi and Alessandro Savorelli, the Mannschaft wear white because the German Football Federation was founded in 1900 when white was the national color of the country between 1867 and 1918 as in the former flag of the German Empire Prussia.
Japan:

Japan's national teams wear the color blue, even though the Japanese flag has no blue in it.
In fact, this color turned into an amulet of luck in Japan after the Japanese football team first wore it in 1936 during the Olympic Games, and defeated the Swedish team 3-2. Ever since, the Japanese sports teams started wearing blue.
Australia:

Everyone, especially football fans living in the Asian continent know that the Australian sports teams, the newcomers to the yellow continent, wear the yellow color despite the fact it is not present on the Australian flag.
The yellow color represents the Acacia pycnantha, which is Australia's national flower found in the continent which is considered a national symbol during the independence process and the unification before 1901.
Venezuela:
There is a huge controversy over why the Venezuelan teams wear dark red. One explanation is that when blending the three colors that make up the Venezuelan flag, blue, yellow and red its product is dark red but this interpretation is not really true because when mixing these these colors it throws up purple.
There are those who say that the dark red color was the color of the Venezuelan army, and the third explanation, which is the most logical, says that the Venezuelan federation wanted to distinguish the colors of the Venezuelan team from that of Colombia and Ecuador.
Kuwait:

The blue sea and sky are important in Kuwait because it shows the connection of the people to pearl hunting as well as the spaciousness of the universe.