My 2 year old seems to have forgotten his colors. He has been mixing up pink and purple and has completely forgotten red and orange. He has known his colors since well before 18 months. Sometimes I think he's messing with me. Saying the wrong color on purpose. He used to do this with animal sounds, but he always had a sly smile and thought it was funny. Now he just gets angry if I try to correct him. He's never had any trouble before. What is going on? Has anyone else experienced this with their little ones?