The problem I have is more with hard and fast rules when it comes to race. I think it's okay to use food to describe skin color/physicality, so long as it's not cliché, i.e. mocha skin or almond eyes. I think most things are okay when done well and thoughtfully! To me, it's more about how your characters live in the story and the writing itself.
When it comes to ethnicity and whether or an author should "fill in the blanks," again, I don't think there is a an absolute answer to that. I mean, immediately stating every non-white character's race when they enter a scene for the first time can feel clunky. But I do think that assuming your reader knows the character's race is a mistake as well, because regardless of the ethnicity of the reader, people have a tendency to default to white when it comes to fictional characters and just in general. There's a great article in Salon called "How Can White Americans Be Free?" by Kartina Richardson. She writes,
Even in California, where white people are not a majority of the population, the L.A. Times and the San Francisco Chronicle both continue to specify race almost exclusively when an individual is non-white. No race specified? Must be a regular person! A white person.
When I read Hunger Games, I assumed Rue was white. I must have just zoomed right over her description and made that assumption-- and I'm both a person of color and a writer. Suzanne Collins told us she had "dark brown skin" and I still just assumed she was white. That's how pervasive that shit is! So when writers say, "I like to let the reader imagine for themselves the race of the characters," I think that's naive and it discounts how deeply we as a society have internalized white default. I also think it's lazy. My ethnicity has so much to do with my identity, with the way I see the world. I think if you as a writer don't make those kinds of decisions, at least in your own head, you haven't fully thought out your characters.
From that same Salon article, Richardson says,
We expect artists of color to address race or we’ll ask why they don’t. White artists are never asked why they aren’t addressing their experience of race in their work. We don’t have the same expectations of white artists because, of course, they are raceless. We assume that if race is not specified and a specific identity is not discussed, then the identity is white.
As an Asian American writer, I am often being asked to justify why I don't write more, or exclusively, Asian stories. What it comes down to is, I want to write the stories I feel like writing, when I feel like writing them. And regardless of whether or not the narrator of my story is Asian American, my experience as an Asian American comes through in a million different ways. My first book Shug is about a 12 year old girl growing up in a small town in the South. Her mother is an alcoholic who is limited in so many ways, and wishes she could do more for her daughter. Shug is young, but she has a lot of burdens and responsibilities that most kids her age don't have. As the child of immigrants, that was my story too. We all tell our own stories the best we can.
First and foremost, I think the writer has to be true to the characters. If the narrator is white, and perhaps sheltered, perhaps didn't grow up in the most diverse town, you have to consider that when you write from their point of view and how they see people. The way I think about race as a second generation Korean American isn't the same way that character thinks about race, and I think the nuances can be really slight and subtle. So, bringing it back to skin color and how we describe race and ethnicity in fiction, we are seeing people through the main character's eyes. As long as the writer is true to that, as cognizant and faithful to that specific point of view, I can't fault them. I think it's really mostly about making decisions with intention and thoughtfulness.