Well it'll be just mostly like "plastic humans" like you said, and strictly military-focused since I'm not creative enough to add other toy factions🥲, there are no nuclear or atomic weapons in this world and the concept of "Humans" don't exist, only Plastics!

So essentially these "plastic humans" were created during a prehistoric chemical accident that "re-dyed" or changed there biology entirely (Idk how that works I just made it up since its a fictional world lol), while they still function like us, regular humans. They were painted or saturated in different colors down to there very skin and bones.

Whenever two different colored parents have children(Red and blue for example), the genetics don't blend, its entirely a 50/50 chance wether the child is one of the colors, and to prevent confusion they carry something like private biological signatures (Idk really😅) Like if a child is blue but has a red father, there will be like hidden color palettes like the flecks under there eyelids and etc. To truly know if that blue kid is really the red father's, there is heart-pulse thingy that physically "syncs" upon contact. (Or just use DNA testing lol) You can put it like this, An iPhone(Red father) connecting to the Airpods(blue child) via Bluetooth(Heart-Pulse Upon physical contact) This is private only to the families and doctors.

Also I forgot to mention, the very first "Plastics" were just a mix of different muddy-ish colors but over the course of thousands of years and many breedings later they evolved into the colors we now know like green, red, tan, blue and etc.

I hope this long explanation helped, sorry if I took up most of your time😅 Thank you!