1. Human male has been 'assigned' to an offworld post, primarily because his family is personae non grata. The planet has a native population of a large race, he befriends one of the natives in his office, and she teaches him her world.
2. Time traveler breaks down in the future. The dominant race of 'Eloi' have been horrible to the lower tech naturalists. The naturalists are a heavier, stronger race, but losing.
He steps in the help the naturalists, and falls in love.
3. Zoologist takes a berth on an interplanetary ship with a mixed race (as in non-terran crew.) Play who you will.