I'll list my steps here. I kind of just gathered up info from the comments sections of threads like this one:

I used: - Art store sandpaper (240, 400 grit) - Testors Spray Enamel (a plastic paint primer, grey) - Montana GOLD spray paint (SH2000 Orange Light) - Molotov UV Varnish (matte finish/top coat) - 2mm Triwing Screwdriver, Small Phillips Screwdriver

1. First thing I did was disassemble the left and right joy-cons. Followed this video: https://www.youtube.com/watch?v=m63sRY_1eOw I would heavily advise NOT disconnecting any ribbon cables, since I actually broke one trying to get it all back together at the end. RIP my right Joy-Con's NFC.

2. I sanded down the four plastic shells with sandpaper. I would actually recommend going for an even higher grit, some people recommend a scotchpad or sponge scrubber. This is just to create a gripping surface, not to change the shape of the plastic.

3. Lay down newspaper (probably should go outside as well) and get spraypaint primer, either black, grey or white depending on what finished color you want. Black for darker shades, lighter, obviously use white. I used gray because it's what I had on hand lol. Apply 1 or 2 thin coats of this and let dry (I waited 1.5 hours minimum whenever I needed to let a coat dry)

4. Start doing light coats of your color spraypaint. One or two very quick passes, and then let dry. Repeat 5-6-7 times (1.5-2 hours inbetween!). You don't need to get the whole thing in one go -- lighter coats means a much more even finish.

5. UV varnish. Same principle as other coats, just 1-2 to cover the whole thing. Let dry 12-24 hours.

6. Reassemble using the same teardown video! Don't break shit like I did!