Purple lips during nap?

My son got a little sick over the weekend. He had a fever, didn’t want to eat (honestly that’s not too different for him), and was a little sleepier than usual. I took him to urgent care Friday. Flu swab was negative and vitals were fine. By Monday, no more fever, personality was completely back and he was eating normally.

Today I took him back to school, and the teacher told me when he woke up from napping she noticed his lips were a little purple-y. Not blue, “a little purple”. I was very alarmed though she didn’t seem to be. He’s in a fantastic mood and has no symptoms at all now... she said he was probably just cold while sleeping and still dehydrated from being sick. She’s not a doctor of course, but I value her opinion as she’s been around children for decades.

What do you think? My son is incredibly pale naturally so I suppose his lips could have looked purple but I’m just like ... wtf.

// EDIT: I am hesitant to take a perfectly healthy-seeming child to the urgent care, because they would just write me off on the basis of something I didn’t even see firsthand. So I called the nurses line and she asked me if he was blue now, how he seemed, if he had any sounds when he breathed. Since he is fine and perky, she said he was probably just cold during his nap, like when you’re in a cold pool.