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.