I made a resource pack that improves the vanilla hay texture by desaturating it and changing the color of the strip around it to brown. Additionally the resource pack adds slabs and stairs for hay blocks by overriding andesite stairs and slabs. There is an optional datapack that overrides the crafting recipes for andesite stairs and slabs so that they now use hay blocks instead of blocks of andesite.
Hope you like it!
If you want to see the blocks in action here are 2 reddit posts I made: