I agree the contrast is quite harsh, and you will have player characters on it, generally speaking characters are usually more contrasting than the environment, the environment should be more passive and subdued in comparison, and if you have too much detail especially coupled with contrastingly detailed it mightn't work, also you could save time rendering that amount of detail, floors should be relatively neutral, walls and props you can usually get away with depicting them quite detailed

really quick edit brightening the dark tone and removing colours from the sand I think 3 tones is plenty, and the contrast shouldn't be too harsh, and a suggestion of how I'd approach sand (it's not tilable though, just a general suggestion)
those trees look rather nice, the twisted trunk especially, if you choose to do dark outlines like that be sure to do the same consistently across other props and objects.