Was Zambia a British colony prior to its independence?

Yes, Zambia was a British colony prior to its independence.

Zambia was formerly known as Northern Rhodesia, and was under British rule from the late 19th century until its independence in 1964. Northern Rhodesia was part of the British South Africa Company's territories in southern Africa, which were later administered by the British Colonial Office. The country gained independence on October 24, 1964, and became the Republic of Zambia.