What is the colored label/part of the RCA jack called?

Heat shrink, right. You want that anyway. Comes in real handy.

nobody sells those colored pieces of plastic... i guess you can buy complete replacement jack and disassemble for needed pieces   

kgbspy, agreed, if the insulators are popping out on my RCA jacks, I would replace the complete jack assemblies if possible.

I’ve have had that happen in the past, but only on lightly made equipment, often a printed circuit board inside, with several pairs of inputs or a board with outputs, the board flexes, things move/loosen/break.

I pay more attention to the quality/solidness of the jacks within that manufacturer’s line, you can check a different model at a store, see if they are strong, before buying something from that manufacturer.

Also, buy returns accepted, out of the box, push/pull/case thickness ... keep or return.

I just pushed like a maniac on my McIntosh preamp from the 60's, probably could take a hammer to them. New 'Chinese' amp, extremely strong, beautiful construction, ...