Nonsense. Nothing to do with colonialism. Sometimes an organisation may chose to employ a msungu so that the msungu can easily network with fellow msungus in other organisations and also donors. Even kenyan flower companies employ msungus from majuu to market their flowers in europe coz a black kenyan from kenya may have difficulties concluding deals na wazungu huko majuu. So yes skin colour can be an asset to a company or organisation and it is purely a commercial decision, not racism or colonialism.
Water is not water, aye? 
Figsed. Like using a luo sales rep in murima. Ama a Kikuyu sales rep in Kisumu. Or a kalenjin sales rep in mandera. The results will be low sales
Many companies also employ yellow yellow receptionists not because they are most qualified but for the image.