On his audio commentary track for The Graduate, Mike Nichols seems rather proud of the fact that he was able to open the film by stating his theme outright. His pride is justified. It's tough to do. Usually the line where a theme is stated will stick out like a sore thumb and turn many people off. Oh that's what they want me to think?! Only truly skilled directors like Nichols are able to pull it off. And the newest filmmaker to join that club is Barry Jenkins.
Not only is Jenkins able to get away with stating his theme outright, he's able to do it while also mentioning the film's title at the same time. That's just asking for trouble! But it works. When Juan tells Little about the Cuban woman who told him that, "In moonlight, black boys look blue" you don't exactly know what to take from that. Sure there's the double meaning of blue as a color and blue as another word for sad, but is that really all there is to this film? Is it just about sadness?
For me the most important aspect of this film is light. This film is filled with different types of light. There is natural light, there is artificial light, there is direct light, there is diffused light, there's warm light, cool light and even highly stylized, colored light. And because this film is nuanced, everyone gets to be seen in a variety of those lights because no person is any one specific thing. In one light they are loving, in another they are hateful. The light can change from scene to scene or angle to angle depending on the emotion of the scene. Sometimes the light can even change within a shot.
So yes, black boys do look blue in the Moonlight. But that's just one type of light.