TIL that the spots some people see while looking at the blue sky is known as the "The Blue Field Entoptic Phenomenon" and is caused by white blood cells moving through the eye.

https://www.aao.org/eye-health/tips-prevention/moving-spots-in-blue-sky#:~:text=What%20Is%20The%20Blue%20Field,cells%20flowing%20through%20your%20eyes.

https://www.reddit.com/r/todayilearned/comments/152l4kr/til_that_the_spots_some_people_see_while_looking/