That's actually very easy. The plastic that changes color when dipped in hot or cold water. It's a gimmick we've seen in modern times with the PusleCon Zartan, and it's not that uncommon in Hot Wheels Cars, both that sort of paint and the UV reactive sort. I'm not sure it's ever been used in a Transformer before, aside from rubsigns?
I also tracked down a set of insecticons, but like the refraktors I also tracked down, at least they're troop builders, so I can still get ER mold Thundercracker and Skywarp to go with my other ER seekers. (I have zero desire to start that collection over, especially at the new scale which I don't care for.)
...I don’t want to go into the troop builder rabbithole
View attachment 30586Grey Bombshell