obviously having both red and green is a nope. would black, white, red, and blue work? or would blue/black be an issue
anyway i think red/black/white/blue works pretty well for the vast majority of people, especially if you make sure the red is lighter than the blue or vice versa.
using coblis:
red-weak/protanomaly:
red-blind/protanopia:
blue-blind/tritanopia:
monochromacy/achromatopsia:

for fire but i'm less sure about water and especially air.
i'd consider the "water drop" shape for water, or maybe a wave? but that might look too much like the fire triangle. maybe a wiggly line representing a set of waves? 𓈖 an egyptian hieroglyph for "water" is the source of the letter M actually
i'm even more unsure about air because obviously you can't, like, see it. my current thought it to imitate some historical "wind being blown out of a face" symbols i've seen and go with a an outward cone of a bunch of slightly wiggly, approximately parallel lines that curl outward at the ends or form a sort of burst or cloud