If I just absolutely need that person to know they are wrong, I will present them with visual or physical proof that they are incorrect without bringing up the previous conversation. For example if someone told me frogs were only green and no other color, I would just say okay and then whenever I talked to them again I would show them photos of different colored frogs and say how cool the different colors were, while never mentioning the previous conversation "hey, I just saw all these different colored frogs! isn't that cool?" (Or something to that effect) . I find that showing someone they are wrong in the moment can cause embarrassment or even anger.. So again, if I feel it is even worth it to correct someone I would do it that way.