When people think of "Heathers" often the first things that comes to mind are the dark comedy aspect, how a lot more people died than we expected, the extremely toxic relationship between Veronica and JD, or the fact that there are three characters named Heather and none of them are the protagonist.
While I do think of those things when I think back on the film, another aspect that's really fascinating to me in the use of color in both the film and in the musical. What's interesting is that each of the main characters are assigned a color, Veronica is blue, Heather Chandler is red, JD is black, Heather Duke is green and Heather McNamara is yellow. Each color that's assigned to them reflects their character.
Blue is a color that is often associated with trust, so it makes sense that our protagonist Veronica would be given the color. Blue is also associated with calmness and intelligence, which Veronica is when compared to other characters like Heather Chandler. Also, in the musical, when Veronica breaks the fourth wall and talks to the audience in a "dear diary" style, the lighting of the stage changes to blue, bringing us into Veronica's thoughts.
Red is a color that can be associated with power and chaos. Heather Chandler is the queen bee of Westerberg high and thrives on her power. Red is also a bright, dominant color witch, again, matched Chandler's personality. What's interesting is that blue is also a powerful color and the two often clash, which is what Chandler and Veronica do. Red is also one of the devil's colors, and Heather Chandler does die. Kurt and Ram, the two jocks are also victims of JD and the main color on their jerseys is red. So it can be assumes in "Heathers" the color red can be used to foreshadow someone's death.
It's pretty easy to guess why JD is associated with black, he's a dark character. Not only is he an abusive boyfriend, but he did also try to blow up a school. Black is perhaps the most dominant and can easily overshadow any color of the rainbow, and it's associated with death. JD wearing a long black trench coat gives him a sort of grim reaper feel, wanting to take everybody's lives, which he does try to do, and it's only because of Veronica that he fails.
Everyone's heard of the phrase "green with envy," well that's exactly what Heather Duke is. At first we may feel bad for her because her "friend" Heather Chandler constantly verbally, and sometimes physically, abuses her. There's a sort of unspoken rivalry between the two of them since Duke in envious of Chandler's power, which is why Chandler may constantly feel the need to put Duke down. After Chandler's death, Duke takes her red scrunchy, symbolizing that she's taking Chandler's power, which Veronica takes for good at the end.
Out of all the Heathers, Heather McNamara is the kindest, which is why her color is yellow. While she does participate in some of the mean things the Heathers do, ultimately she's loyal to her friends and just wants them to be happy (a true Hufflepuff). Yellow is also a much less dominant color, symbolizing McNamara's lack of desire for power, this is why Chandler never abused her the way she did to Duke.
The only other significant character who wears a soft color is Martha (who plays a much more significant role in the musical than in the film). In the musical she wears a light pink color, symbolizing her innocence to how the social structure of her school really works. What's interesting about her and McNamara is that they both attempt to commit suicide because they thought it would fix their problems, seeing as Heather Chandler and Kurt and Ram gained even more popularity from their supposed "suicides." Both the soft colors were overwhelmed enough that they tried to take their own lives, and it's only because Martha's attempt failed and McNamara was saved by Veronica that they both live to the end.
There's a lot more I could say about both the Heathers film and musical, but if I did that we would be here forever. "Heathers" has a lot to offer, but I really wanted to focus on how it cleverly uses color to reflect the characters.