AppleofEden released a nifty little mod called Skyrim Stardust that makes the sky "rain stardust" when it's clear. It makes Skyrim look more magical and sparkly. TehPikachuHat added an optional texture that makes the base game's silver diamonds into blue-white puffs. Nicer, but I decided I wanted the "falling magic" to look different, so I changed it to my tastes: smaller and multicolored, to match with the various auroras that can occur. I haven't yet figured out where the base game uses this texture (sparks from hitting glaciers?), but if the idea of a rainbow effect bothers you, just remember that ice shards are refractive, so they can actually look like rainbow sparkles for a moment. Consider it exaggerated for stylistic reasons (or just remove this texture and use one that suits you).

Comes in three flavors: lite, regular, and heavy. Lite is nearly invisible unless against a dark background, but doesn't tend to show clumps as readily; regular and heavy are denser, so they show up more readily, but clumps are more visible (the clumping is a problem with the .esp, and as of 2020, hasn't been resolved - it just randomly clumps together sometimes). More specifically, regular is twice as dense as lite, and heavy is four times as dense as lite (twice as dense as regular).
There's also a pair of optional white files, one that shows up as almost pure white (but has hints of color) and one that's blended with the lite rainbow main file to produce a more vivid and colorful result; these are for people who find the saturation of the main files to simply be too much.

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Looks nice with...
Skygazer - Constellations
Moon Glow
Ethereal Cosmos (though I swap the galaxy with the one from Purity)
ETHEREAL AURORAS
AURORA