My fav blue thing that I saw is probably this cobalt blue fungus (Terana coerulea).
The deep blue it produces is so striking that it looks like a color that shouldn’t exist.
https://www.inaturalist.org/observations/259968491
Also, I love forget-me-nots, so I have to add one, but they are so difficult to ID to species level.
https://www.inaturalist.org/observations/159639583