The issue with the African colonies is that European monarchies often simply came and destroyed the existing hierarchy and imposed unilateral colonial administration, not based on pre-existing states or tribes but what was convenient for the Europeans at the time. Often whatever monarchs refused to bow to the colonial jackboot was just destroyed. The German Kamerun and Vichy French Africa are the best example of an African colony left to its own devices on day-to-day affairs.
My ideal solution would have been something like the early colonial ambitions: small settlements, limited to the coasts, and Europeans actually treating preexisting African kingdoms like actual states instead of vassals to be lorded over. In exchange for protection and military aid, as well as access to European markets and education, African rulers would swear fealty to a European monarch, pledging to support them in wars, protecting merchants, offering tribute, contributing a certain number of soldiers, etc. A system such as this one would've easily out lasted the past colonial projects of this timeline. In fact, when looking at it as a whole its no surprise that the age of New Colonialism lasted only for about 50 years.