Did you upgraded your catalog or you import the older one to new catalog* in Lightroom 6?
*If so while importing you should have "Apply during import" in Panel on the right set t none
Does this happens when you switch from Library to Develop module?
Just to be sure make sure a Preset is not highlighted
Also go though this article once Why does the color and or tone of my image change after import?
Let us know if that helps