Was it the stories of his wealth that attracted colonialists or was it something else? Especially since West Africa was arguably one of the richest regions in the world, is he the reason that it's so poor now, or is it to do with something else?
One reason why the Portuguese started exploring down the West African coast, which led to its eventual colonisation by European countries, was because they knew from contact with the Muslim world in North Africa that it was a significant source of gold. Notably the Portuguese conquered Ceuta (in Morocco) in 1415, which was one of the end points of the Trans-Saharan gold trade. Under the direction of Prince Henry (1394 – 1460) 'the navigator', they started exploring the coast by sea, reaching Senegal by 1444. It's possible that stories of Mansa Musa were current at the time, but even if so, this certainly wasn't their only source of knowledge about the gold trade.