Of the five hats, only 2 are red 1 yellow, 2 are yellow 1 red, and 3 are from Huang San. If Xiao Ming sees two red hats, he can judge that his hat is yellow, then Xiao Ming sees 1 red 1 yellow or 2 yellow; Later, Xiao Liang judged that because of Xiaoming's words, Xiao Liang could determine whether he and Xiaodong were 1 red 1 yellow or 2 yellow. At this time, he can see the color of Xiaodong's hat, but he can't judge the color of the hat, only to prove that he saw Xiaodong's hat was yellow, which is how Xiaodong judged it.