What are Arrows?

Perhaps there was a big war before the timeline of the game, when the species were trying to get settled into some form of 'government'. Bows and arrows were frequently used because if your aim was good it didn't matter if another species was faster than you or could fly and you couldn't (though how they used them without thumbs I don't know but doesn't matter). After the dust of the war settled, they needed some kind of currency and hey, look at all of these arrow heads that every species has.
Perhaps the different kinds come from the fact that species living in different environments used different metals and rocks to make their heads? They valued the different materials and so maybe gold is worth 20 silver or whatever.

I also think that judging by the fact that gold and silver share the same texture but blue has a different, more smooth one, that blue is either worth way less than the others or worth way more. Probably less because of how you arranged them and how people tend to progress from left to right, and because in that image of your total money the image shown is the blue one so it would make sense that's the lowest value.
Like seen in Legend of Zelda here, green rupees are the least valuable (though this would probably have been answered if I had ever played the game before LOL)

They're definitely arrowheads! Or they look a lot like them at least :')
I don't really have ideas for them lore-wise that people haven't already said above, but I can see one of the three types being the most common (like the blue-ish one) and the gold/silver ones being rarer. Like one gold one could be equal to say, 1000 blue arrows. It'd be neat if you could exchange your blue arrows for gold/silver ones, or vice versa