These are more related to the dying process than the anodization (which builds up the oxide layer that can accept dyes).
To do a fade you dip the entire yoyo in one color, then half of it in another color, and they mix. The colors are subtractive, like paints, rather than additive like lights. So, if you want a pink/purple fade, you dip it 100% in pink first, then 50% in aqua.
If you want pink/purple/aqua (unicorn fade) you dip it 60% in pink, then 60% in aqua from the other side.
Let’s say you want unicorn fade splash over black, instead.
First you made the full 100% unicorn fade. Then you mask off some of it by splashing whatever masking compound you’re using on it. Then you dip the whole thing in a solution that removes the color everywhere that ISN’T masked. This solution might be bleach or acid.
Then you can dip the whole thing in black or whatever color you want the background to be.
“Clear” or silver anodization is simply without any dyes, so the natural color of the aluminum + the surface treatment (tumbled, blasted) shows through.
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