Colombia, the country. Columbia, the university. I have a guide to either the 1970 or '74 World Cup in which it is spelt 'Columbia.' That spelling is now seen as archaic, I think. Edit: I am wrong about the book. It mentions 'Rumania' and not 'Columbia...'
100% Colombia as per sister in law who is married to a Colombian and lives in Colombia. It's never been Columbia.