"France probably had the most intermarriage with their colonial people" -- I always thought the French were aloof (Vietnam, Algeria, West AFrica) compared to the Spanish.
Britain’s system was actually ingenious, and probably the reason why their empire outlasted so many others (and kept close ties even after independence). They would take a dominant group (Zulus, for instance), and basically use them to control the situation on the ground in return for a higher standard of living. The legacy of this policy in South Africa is the antagonism between the ANC and the Zulus, who have their own hierarchy; the Zulus have lost some of the status they enjoyed in the colony. When independence eventually came (usually without the violence of Angola or Algeria), many saw benefits to keeping close ties with Britain.
The French intermarried a lot in Canada and Vietnam; I haven’t heard much about it in West Africa or the Caribbean, so probably not much. The Spanish themselves had a lot of intermarriage early on, but to this day much of the upper classes in Hispanic countries is pure Spanish blood. As these countries revert to “native” rule (Cuba, Venezuela), some of those people take the opportunity to return to Spain.