Can understand the confusion with shield mechanic. I was close to simplifying it to just matching colors, but felt that this wasn’t alchem-y enough, so I settled on opposing elements destroy each other.
Choosing colors was a pain in the butt, because for example brown for earth could be confused with orange for fire. I realized way too late that I can just make projectiles themselves a different shape depending on element, instead of using teeny-tiny symbols that are not even visible.