If the print quality is good, scotchbrite or 2000 grit paper would work.
Prefer wet sanding because wet sanding reduces the amount of dust and keeps the temperature down. Assuming PLA.
Try not to print with PLA, it's not a high quality material. Prefer ASA or PA, but most printers can't do PA.
Get an automotive primer for the undercoat, then sand again.
Go to an art supplies store to get the two tone paint. Specifically you want something used for street art.
For two tone, use a thick coat then a light coat. The light coat has a light sheene.
If spray straight on doesn't feel right, you can spray into a cup then use a brush.
Quick google, Citidel, Molatol, and MTN may have these. Resene has an automotive section, so going there would be an option.
Add a clear coat to the outside to protect the paint so it doesn't rub off.