This happens every wintertime for me as blue string lights are put up, and they always appear “fuzzy” compared to other colors.
Now I understand why blue in particular. Damage is done, I wish I could take it back.
Stars are unimaginably small point lights in the sky. They look like larger dots because of imperfect focus in our eyes [1]. But since they are in fact so tiny, it means very small atmospheric variation and obstruction—heat shimmer, floating dust, etc.—can significantly momentarily occlude the star. That causes its perceived brightness to vary over time.