This is required due to the addition of the MoveUnretraction segment type in the engine. Those moves need to be displayed as travel moves, with a new color.
CURA-11830
We can't change this index to an integer, because varying variables can't be integer, even though this variable will only really be tested on vertex level. Not sure if varying was the right choice, but I don't want to change that.
This prevents a crash, probably only occurring on certain GPUs.
Contributes to issue CURA-8657.