don't eat (the) yellow snow

humorous A warning against eating snow that has been urinated on (and thus is yellow, not white). OK, fine, you kids can go play outside—but don't eat yellow snow! Please keep a close eye on your baby sister. I can't exactly tell her, "Don't eat the yellow snow"—she won't understand. You catch falling snowflakes with your tongue, you don't eat the snow that's already on the ground! And you definitely don't eat yellow snow!