I watched the movie carefully but still can't guess what is the meaning of the title Tangerine (2015).
A few articles, such as this one from The Independent claim it is due to the production process:
As for the film’s title, Tangerine was chosen after orange became the dominant colour when the saturation was pumped up in post-production.
They provide the following quote from the director (Sean Baker) to back this up:
“The world [in the movie] is so colourful and the women are so colourful,” said Baker. “We wanted to match them.”
However, the director has addressed this explicitly in a different interview:
Question: I’ve wondered about this ever since I saw the movie, and I’ve read a few different theories online, but why did you decide to call the movie “Tangerine”?
Answer: We had a bunch of titles and that was one that everybody kept coming back to. It resonated with everybody, and everyone has their own interpretation. It doesn’t really stem from the dominant hue of the film, but there’s something about the title that reminds me of Christmas. I think I used to get tangerines in my stocking on Christmas, so there was a personal link for me. There are hints throughout the film, like the air freshener in the cab. It’s funny, filmmakers are the only artists who feel obligated to title their works of art. Musicians and poets and novelists don’t have to, but we’re the only ones who feel obligated, like we have to, and I want to get away from that. I’m fine with a title that’s open to interpretation.