Blacks would and did benefit greatly when colonialism was a standard third world model. There is not one successful black-majority country in the world. If you point to South Africa you must also allow for its death spiral.
One of the good things about colonialism, particularly that of the British Empire, was that it connected people through common language, law, education, military training, medicine, railroads, and most of all, the advancement of Christianity. What would India look like today had the British not provided a unifying umbrella for that huge diverse population?
There are exceptions to that, Belgium in the Congo being a major one but mostly that is true.