A colony is an appropriation a Mandate is a charge.
Colonies started a long time ago as trade counters scattered along the coast of Africa and Southern Asia. As commerce developped with the Spice’s Islands, boats needed logistic harbours where to drop anchor on the way. From these “bridge heads” Portugal, but mainly France and Britain, moved inland to conquer a territory to exploit for human and mineral resources. The number and nature of the subterfuges used to justify the colonial conquest are too many to enumerate.
The notion of mandate was devised originally by the Society of Nations, but further developped by the United Nations. An “advanced” nation (such as France or Britain for some reason) would be charged by the World Congress to administer an “underdevelopped” one and bring it to an acceptable level of civilization. Tenure for a Colony was determined by the balance between the armed forces of the two parties. Tenure for a Mandate was (and still is in some rare cases) defined at the onset and limted to a number of years.