This started out as a comment, but got too big and I decided to change it into an answer, focusing on the OP's last question:
But is it, I don't know, somehow alienating or offensive to white readers that the characters aren't white, and that no main characters are white?
Being white or dark-skinned depends a lot on culture. I'm from Southern Europe and I consider my skin rather light. While in the UK for a spell, I was told my skin was dark and my first thought was 'are these people colour blind?' - if you draw your face and paint it using a light coloured pencil, then the skin isn't dark, it's light. It makes no difference if you're from China, Mexico or Norway. The skin is light coloured.
Anyway, I feel the obsession with breaking down people by race (Hispanic, black, Chinese) is annoying, whether it's done in a racist or an inclusive way. Do we really look at a person and the first impression we get is their race? Yes, I admit that I notice skin colour, much like I notice hair colour, but race? We're not in the 19th century anymore to talk about races like they're a real thing! The only reason I notice skin colour is because it's a distinguishing feature on par with hair colour and length, or eye colour, not because it makes someone a different race.
To answer your question, to see light skinned people called non-white (in films or TV) is annoying to the point of pulling me out of a story. It's one of the things I most hate in a lot of American based story-telling: everything boils down to white and non-white, with non-white being specifically termed Hispanic, Arabic or whatever. How can people even tell where one (or one's parents or grandparents) are from? When I'm reading a novel, having characters described as Hyspanic does feel alienating because even within an ethnic group there is a wide variety of appearance, both in skin tone and hair colour.
It is so, SO refreshing when a story ignores all that and simply treats characters as normal people, even if they're described as having light or dark skin (because of visualising their image, not because they're part of a race or a mixed race or whatever).
Do write a refreshing book in that aspect, please. Especially if the story is not supposed to focus on racism.
Edit in reaction to some comments:
I'm very much aware of racism, make no mistake. I know that people will discriminate based on skin tone and ethnic background and I do not think that particular reality should be ignored or overlooked in fiction. However, if a story is not supposed to tackle racism, then why must characters be characterised into 'races'? That was the point I (may have) failed to make clearly.
Allow me to present it in a different view: if we have a story set in current day USA and if the characters are 'racially categorising' each other, then it makes sense to present a character as Hispanic because that is how the world within that narrative sees the character.
But if the story is set elsewhere or in a futuristic post-apocalyptic world where race is not a thing anymore, or even in a present day location where locals do not do racial profiling, then presenting a character as Hispanic will be inserting the racial categorisation that doesn't exist within the fictional world.
The reason why the constant 'racial profiling' annoys me is that it expects me, the reader, to see the character first and foremost as the race they supposedly belong to. Tell me a character's family is Mexican or that a character is black as a way to physically describe an individual character, not as the moniker I'll remember them by. To use the OP's example, I do not want to remember Analise as the Hispanic or Poet as the black person. I want to remember Analise as the one who makes silly jokes and Poet as the one who is always on the look out for old books.
Again, even though I live in a sheltered area, I am still much aware of racism around me, so I have to wonder: if one wants to diminish racism, why keep on using race as the main descriptor or identifier of a character. Let them be individuals we can relate to despite skin colour.
And my appologies for the long rant.