Alright, I went back and compared two screen shots. The color palet isn't that different, but the screen shots on Grim Dawn do seem to have more texture. If Diablo 3 screen shot have more texture, they should look fairly more grim. Without texture, the world of Diablo 3 looks very smooth.
I took this screenshot to compare
http://us.blizzard.com/diablo3/media/screenshots.xml#133
The rocks don't have that same crisp detail as in the Grim Dawn's screen shots.
http://www.grimdawn.com/screenshots/2010-07-24_fallingarch_lrg.jpg