Since 1.19.4 added data-driven data types, it could be handy to test what kind of damage type a weapon or projectile uses.
Since this won't be useful for most end-users, maybe it could be F3 or gamerule only.

You can already do this. Mod always showed different colour for each damave type

I didn't notice that 😅, but I was referring to the IDs/ResourceLocation of damage types, like if I were to add one via a mod.

This can be added via config