As someone who uses arrows a fair bit, I’m kind of amazed that there isn’t an easier way to tell them apart a glance without hovering over them in the inventory/quick slots (at least for those of us on consoles), as a lot of their thumbnails look a lot alike.
My idea is -seeing as you can’t apply attachments to ammunition anyway- is perhaps some kind of background behind some of the specialist ammunition types, or even a color burst, like green (or green gas cloud) for poison gas arrows, yellow (or yellow flame/explosion image) for explosive arrows, purple for healing arrows, maybe the oil thumbnail pic behind the oil arrows.
Even a white burst for Light arrows maybe.