What colonialism are you talking about? You began by talking about the Norman conquest of Britain; white people conquering other white people: yet you still miss the point. Africans have always been colonised, just like Europeans. It is just that before the so called “scramble for Africa,” Africa was colonised by other Africans. The slave empires in Africa were the world centres of the slave trade long before any white men showed up.
So yes: It was not about race. It was about greed and power. But when you talk about colonisation you only mean white colonisation, which kind of betrays the fact that for you, it very much is about race. You are, I assume talking about the European competition to colonise Africa which began in the late 1800s; just for the record long after slavery had already been abolished across Europe and even in America.
The Europeans did not invent slavery; although relatively small numbers of them participated in it too; just like the Africans did; but the Europeans were also the first to abolish it despite the resistance of the African kingdoms which fought hard to preserve it.
History is not so black and white as you would like to believe. You can only believe that if you really do think eveything is about race. Inhumanity does not have a skin colour. It has been perpetrated by and against all races. So yes, as another poster here has already said; if you want to have any kind of constructive conversation, you need to remove the emotion from the argument and study the facts objectively. Cherry picking your “good guys” and “bad guys” based simply on race is stupid, immature and frankly racist.