[Note: The following information comes from a postby a representative of Valyrian Steel, licensed creators of replica weapons and armor based on A Song of Ice and Fire and HBO's Game of Thrones.
Actually... GRRM doesn't like HBO's arakhs. I thought, and HBO thought (I suppose), and many people thought, that because of the kh consonant group and the descriptions, he modeled arakhs after khopeshes, which is not an invented type of sword. HBO arakhs are basically khopeshes. It seemed to me personally these shape of sword would do well from horseback.I thought for sure I had it pegged down, all while reading I always pictured a khopesh.
I told as much to GRRM and he corrected me, in his book version, arakhs are more like scimitars, though what you may think of as a scimitar is far less than what he explained. Something more like this. A very significant curve.
If we have our way we'll do both versions.
As for Dawn, in the books it has a milky white blade. We do not know a way to mimic that without using paint, and GRRM doesn't like paint.