Air taxi pilot reported the loss of the primary flight display and while descending through instrument conditions they inadvertently entered into a 20 degree bank. The pilot corrected the flight path and continued to a safe landing.

Narrative

Shortly after reaching my cruising altitude of 13000 ft. MSL; the primary flight display (PFD) on the G600 turned solid white then displayed rainbow colored lines horizontally across the display. I was in visual conditions above a thin layer of clouds. I immediately notified air traffic control (ATC) of the event and advised them that I would attempt to troubleshoot the issue. I turned off the power to the G600 to reset the system; then back on. Once it powered up again; the issue remained unchanged. After taking a moment to think of the best course of action to take; I requested to return to ZZZ. I was able to safely operate the aircraft by reference to the back up instruments. Considering the nature of the situation; it was in my judgment that I deemed this situation to be a potential threat to the safety of flight. Therefore I [requested priority handling] and notified ATC. During decent through instrument conditions; there was a brief moment I was distracted by my iPad to begin briefing the return to ZZZ. I was hand flying the aircraft; because the autopilot was not operable due to the PFD failure. When I looked back to scan my instruments; I immediately recognized I was in a 20 degree bank to the left. I corrected with smooth even control pressure and returned to the assigned heading. ATC did ask me about the deviation; nearly after the fact. I told them that I had corrected and was on the assigned heading again. No other deviations occurred. The flight resulted in a safe landing back at ZZZ with no other events to report. Suggestion: I only have one suggestion and it is to myself. During any phase of flight; [priority handling] or not; it is imperative that the omission of any instrument during my scan be recognized immediately and corrected so as to avoid a usual attitude situation.