>>10367350nta, I've only painted Gyarados as far as pokepla go, so amateur here.
Since it's Bandai I assumed it was the same plastic as Gunpla, so I spray-painted most of the metallic red as-is with a marker airbrush.
Had to paint one section by hand as I ran out of air, which is quite noticeable up close.
Yellows were mostly sprayed with a normal airbrush, tamiya paint, also as-is. But I put too much thinner in so spraying got messy lol.
In the end, it turned out alright. Only paint peel it has is because of my own stupidity of messing around with it too early. Got it disassembled again atm because I still have to topcoat.
You should probably use primer first though, esp if you want to use lighter colors on dark.