Praise then darkness and Creation unfinished. - Estraven
So!
Left Hand of Darkness by Ursula K. Le Guin.
Basic idea is that Main Charecter A, Genly Ai ( or called Genry Ai thoughout the book as he's the only one that can differentiate the l and r. ) is a bit of a secular missionary for the Ekumenican Confedertion, which is a loose association of different planets for the purposes of the trading of material goods and information. Genry is from Earth - and by this time most people have learned telepathy as well. ( I say this because I though Genry was from another alien planet until almost the end of the book, until he says something about his ancestors on Earth. )
So Mr. Ai is trying to get Genthen to accept that they are not alone, with the sorta kinda help of Main Character B. Who is mostly called Estraven, but it's like calling Rodrick Spode 'Sidcup.' I say "kinda sorta" as they both have different agendas for having Genthen join the confederation.
( The plot - that I could follow, at least. )But what really makes it sci-fi - other than it being an alien planet - is that the people of Genthen are... trigendered? They have a monthly sexual cycle ( kemmer ) where they go from neuter ( sommer ) to either male or female. The exact sex they shift into depends on if there's a male or female about. About half the time Genly doesn't know how to describe the people he meets. ( Neither, actually, does Le Guin, as she admits in the afterword. )
This would be the book the line "The King was pregnant." came from.
It's world building is excellent - and even though the plot was all political theater, when it got too bogged down in backstabbing of factions that were just introduced two paragraphs earlier, it breaks for a myth. It's a good book.
And, also cool? There is not a single white person in the entire book.