I'm going off the cuff rn, and will bring up canon quotes later *but* I think that east of the source of the Green blood should be scrubbed clean of sand dunes of any kind and replaced with dry plains, scrubland and rocky desert thats more hospitable and traversable (but not ideal) than the dune deserts of Hellholt and Sandstone. Desert ecosystems are some of the most fascinating and dynamic ecosystems on the planet with no 2 deserts looking the same, and Dorne has the opportunity to depict the difference between the sand deserts in the West and the scrubby deserts and scrublands of the East.
The greenblood needs to be a much more significant river, but also shallower (its described as being a lesser river than the Mander by Arianne but considering the Mander thats not a hard thing to occur). It should be emblematic as
the lifeblood of Dorne, the greatest source of life in what would otherwise be a tough to live area. I think we should avoid it looking too Egyptian and try for some different feelings that feel Dornish but not Essossi.
In terms of biome coloring for desert biomes, I think my main issue is that grass blocks are
blue like almost Riverlands grass blue when I'd prefer a
slightly (and I mean subtle af) yellower variant on mushroom_island grass. Grass that looks like its been exposed to sunlight a bit more harshly but isn't fucking dead. Because rn whenever I do terraforming for grass at The Tor, hidden spots of desert biome turn my leaves dark green and grass blue (with sandy grass remaining the correct color) instead of the lovely light greens that Mushroom_island provides.
In conclusion:
Eastern Sand Dunes Delenda Est