It dont think it looks like greenscreen. At all. 
Theyve just blown out the whites in the cinematography  for some reason. Usually that happens with cheap cameras, inexperienced DOPs, or poor lighting. Supernatural  in its early seasons kept the colors low, blew out the  whites while also crushing blacks. When they upgraded  their cameras and could afford better lighting the show dropped that look. This is one reason Bastard looks like a SyFy show. SyFy shows  usually have  low budgets and use lower quality lighting and equipment which results in some blown out ugly cinematography.  Tho in this day and age with digital cameras its less of an issue providing the DOP knows his or her way around lighting.
 Surely the budget was good enough to afford better cinematography for Bastard Executioner.  So this must be an artistic choice by Sutter, but why Sutter would deliberately  pick this sort of look for this show is beyond me.
Damn. Was really hoping this would be something special.
