Was Singapore a British Colony?

Yes, Singapore was in fact a British colony. This type of political relationship began in 1819 and was spearheaded by a Lieutenant-Governor of the British Empire named Sir Stamford Raffles (1781-1826).

During World War II, from the years of 1942 to 1945, Singapore was actually occupied by Japan. And after the Allied Forces emerged victorious from the War (i.e. Japan surrendered), Singapore was cast into a state of disorder in which there was no clear government in charge. Eventually the British reestablished their presence in the nation.  However, by this time the damage had already been done, as Britain was no longer perceived as an invincible force in the eyes of the people of Singapore. Moreover with this indeed being post-WWII, as with other parts of the world, Singaporeans themselves began to become more anti-colonial and nationalistic. So the days of British rule were nearing their end.

Ultimately, the British colonization of Singapore is considered to have officially ended in 1963. That was the year when the country we know as Malaysia adopted its current name. And at the time it included Singapore amongst its states. So for all intents and purposes, according to history Singapore was actually a colony of Britain for 144 years. This was from 1819 to 1963.