Blue is such a strange color. It hardly occurs normally in nature and is quite unnatural to see. Think about how a lot of spaceships have blue accents and are mostly silver. You know how there's blue macaws? Their feathers are actually green but are displayed in a way, due to the specific structure of the their feathers, that makes them appear blue. They sky isn't even blue, it's just our eyes and light jointly playing tricks on us. That's why I think it's so hard for people to get the exact shade of blue for the sky because it's not actually blue but it looks blue. Same with water too. People really like the color blue and surround ourselves with it but in nature, it's an alien color. The only thing I can think of is lapis lazuli, that is naturally blue. That's also why blue wasn't really seen in dyes in early times and I think that's really interesting.
Overall Thought:
LOOK OUT YOUR WINDOW