World Building: Each race has a certain set of skills/personality traits, which correlate to what color hair and eyes they have. 

Yellow = Government/Leadership Roles. They're leaders, charismatic, friendly, and happy.

Red = Farmers/Soldiers/Civilians. They're strong, stocky, and reliable. 

Green = Strategists/Scholars/Scientists. They're smart, less emotional, and blunt.

Blue = Civilians/Celebrities/Entertainers. They're friendly, partiers, and talented at the arts.

Natural contrasts are Blue vs Green (Art vs Science) and Red vs Yellow (Followers vs Leaders). 

The yellows found out a while ago that if a certain melody was played, they'd forget all sad/unhappy/angry memories. They do this to help with depression and the struggles of making hard decisions. It doesn't work on the other ones. When a child is born between two different races, the child is randomly assigned to one of the races. 

Prompt: Main character A is a mix between yellow and green, but they didn't just switch to one of the races. Their eyes are yellow, and their hair is green. After a lot of questions and pesky researchers in A's younger days, they decide to dye their hair yellow to prevent any questions. They also see to have traits from both races. They figure out the yellow melody, and find out that it doesn't work on them. They debate whether to tell their other yellow friends. 

Notes: When I first thought of this, A was a girl and she wanted to tell her green friend about it. Also, mutant mixes like her were killed, but that's waaay too cliche. This story could be a dramatic slice of life story or a romance, or something else. It's a little open plot-wise.