Now that you own it, make sure you take proper care of it. When was the last time the oil was changed? What about the engine and cabin air filters? If you bought it from a dealer, these items might be new. If you bought it from a private party, I’d doubt they changed them recently. Oil color doesn’t usually indicate it needs to be changed. Since this car is new to you, black oil should mean to change it immediately since you can’t be sure when it was changed.