Do me a favor. Open up your manuscript and search for the word "dark." What do you notice? Are you using it literally as a physical descriptor? Figuratively, as a way to describe a mood or tone? Perhaps both? Are you noticing any trends, patterns, or maybe some problems with how you're using the word?
Dark is one of those words that has loaded meaning and doesn't exist without it's implied or explicit counterpart, light. Words alone are not problems but how we choose to use them. What we imply, what we leave out, what we mean, and what can be inferred by the use of a word is where things get tricky.
Physical descriptor
Character Descriptions
Their dark skin was dripping in sweat. A fine sentence (that I just made up), which wouldn't at first glance raise any eyebrows. The trouble with the usage of "dark" here is the writer isn't taking into account that dark is 1. subjective 2. relative and on its own, usually not enough information for your reader.
These colors are dark but are not human skin tones
Their skin is dark...
If you compare it to them...
But how about them?
I think you get the point. Dark is the absence of light. If you're using dark as a physical descriptor it cannot stand alone. You need a noun to help your reader see what you're describing. Let's try that sentence again.
Their dark blue skin was dripping with sweat. Now I know what you're talking about!
Tone/Mood Descriptor
Somebody told a lie one day. They couched it in language. They made everything Black ugly and evil. Look in your dictionaries and see the synonyms of the word Black. It’s always something degrading and low and sinister. Look at the word White, it’s always something pure, high and clean. - Martin Luther King Jr.
In literature, a common symbol is using dark to mean bad/negative/evil and light to mean good/positive/righteous.
We see it in words like black magic or a black day. Or in stories, Darth Vader clad in black, and Luke Skywalker wears white. or even in The Lion King, Scar is a dark shade than Mufasa and Simba.
It's difficult to figure out what came first, the chicken or egg. Or in this case, has the symbolism seeped into our collective culture from literature, or has our bigoted culture infiltrated our literature? But that isn't the point, when girls with darker-skinned are more harshly punished in school and preferential job treatment is given to lighter-skinned applicants it is harmful to perpetuate this trope even if your story feels unrelated to these issues. As writers, we cannot continue to give validity to and expose readers to this dichotomy.
Something that is less common in modern writing but still happens, to vary up the word choice an author may choose to use the word "black" as a direct synonym for "dark."
For example: “Stars, hide your fires; Let not light see my black and deep desires.” ― William Shakespeare, Macbeth
This usage for black should be avoided because it more directly and harshly makes that connection between black and evil/bad.
How do you fix this?
Go back to that word search in your manuscript. Scrutinize your use of the words "black," "dark," "white," and "light."
Are they used symbolically to represent good and evil in this traditional way? If so think about subverting that definition and literally flipping it around. Can you use other contrasting colors or symbols to represent the tone you're trying to convey?
Can you find other synonyms or symbols to use instead of these words/images? For example, "white" can mean cold, sterile, and bland. While "black" can mean, pride, elegance, and sophistication.
Ask your sensitivity reader to take a look at your manuscript and help you think of some alternatives.