Accordning to a Gaming Bolt interview with Balazs Torok, Lead Engine Programmer for The Witcher 3: Wild Hunt, there won't be any differences in graphics between Playstation 4 and Xbox One. CD Projekt Red has, according to him, chosen not to use any console specific features to get the most similar result possible:
"CD Projekt are trying to deliver the same experience across the Playstation 4 and Xbox One. Despite their similarities, the PS4 and Xbox One do have some decidedly unique hardware features."
"We always want to provide the best possible experience to all our gamers regardless of the platform and so we are not aiming to develop special graphical features for any of them."