Cannabis (1970)

Starts with a slim blonde teen standing indoors by a mirror, then walking outside in natural light. The setting shifts to a lab with a guy in his 30s standing under bright lights. The real action begins when the blonde returns indoors, joining a brunette with wavy hair for a steamy threesome. They embrace intimately, hinting at foreplay, but nothing explicit is shown. The lab scene breaks the flow, but the close-ups of the threesome make it worthwhile. Dim, warm lighting adds to the mood.