Wicked, Wicked (1973)

"Duo-Vision. No Glasses - All You Need Are Your Eyes."

Simmons, the manager of a seaside hotel in California, has a problem: Guests are turning up dead, and Sgt. Ramsey, the hotel's detective, has no information as to the identity of the murderer. The only thing anybody knows is that the killer wears a strange mask and has a fondness for blonde women. As Ramsey tracks down a list of suspects that includes the hotel handyman, Lisa, the hotel's lounge singer, finds herself in danger.