It will probably take a couple of oil changes for the colour of the oil to look clean straight away. Usually when oil has turned black and sludgey is when people dont do regular oil changes and leave the same oil in there for months on end, sometimes up to 50,000k's :nonono: That is not good practice if you want your motor to last.
You can get additives that get rid of most of the black oil, but its usually best to use it before you do your oil change. Ive heard of people using cheap non brand name oils to chuck in for a couple k's or so to help condition the inside of the motor again, then change the oil and put decent stuff in.