According to Snopes.com- Yes Bobby Kennedy, Attorney General at the time, did predict a black President, but he used the world "colored" in the statement. The times they have a-changed!
He Gave a speech to the Voice of America all around the world 40 years ago. and despite what was going on in the country, particularly in Alabama, Bobby Kennedy said this: Things are 'moving so fast in race relations a Negro could be president in 40 Years' ( This is in 1968, its 2008 Now) 'There is no question about it' the attorney general said ' In the next 40 years a Negro can achieve the same position that my brother has'....Kennedy said that prejudice exists and probably will continue to....' But we have tried to make progress and we are making progress. We are not going to accept the satus quo.'
(note:I have been corrected- the original speech was given in 1961 according to Snopes, so he was a couple years off... it's still amazing having lived thru Camelot)