We constantly talk about red flags and deal-breakers here, but what about your yellow flags?

What is a trait or behavior a date could have that would make you pause and delve deeper into the "why" of it, or something you don't necessarily like but would be okay living with if you got serious? Have you ever had a yellow flag turn into a red flag after learning more about the person? How about a green flag, after seeing it's not such a big deal?