Would you mind terribly converting the terrain to a mesh, baking, and showing us how that looks?
I’m having trouble seeing why you feel the color is different than what you think it should be.
It’s 100% possible, I just don’t clearly see anything that points to anything being wildly bad / not what I would expect.
One thing that could be missing for rivers is reflection captures- this shouldn’t really change the darkness of the landscape vs the same(or similar) static mesh though.