A few suggestions for what they are worth, from another forum. Interracial couples, not necessarily nudity or sex:
Under the Cherry Moon (1986) Prince & Kristin Scott Thomas
White Lie (1991) Gregory Hines & Annette O'Toole
The Annihilation of Fish (1999) James Earl Jones & Lynn Redgrave
Far From Heaven (2002) Dennis Haysbert & Julianne Moore
Death Wish II (1982) Laurence Fishburne (et al.) & Robin Sherwood
The Great White Hope (1970) James Earl Jones & Jane Alexander
The Story of a Three-Day Pass (1968) Harry Baird & Nicole Berger