How did Dalton discover color blindness?
The reason is that Dalton has no concept of pink at all. He just wanted to buy a pair of gray socks, but because pink is gray in his eyes, he took a pair of pink socks by mistake. I didn't notice it either (of course, the salesman won't remind me of the interest of the guests). It was not until his grandmother found out that he knew that his color vision was different from others.