Adding the different-colored popcorns on Rnd13 is easy, but adds four additional ends per side.

1. On the last sc before fold the popcorn color (PC) into a loop with a decent-sized tail. Catch the PC loop instead of colorA and drop colorA to the back.
2. Work the Ext PC as-written, but fold colorA into a loop and use it for the closing chain.
3. Drop PC to the back and cut a decent-sized tail for it.