Image imported from derpibooru 
Original Description:
 
I needed to, apparently, give this color. Let it be known that I enjoy symbolism a lot. Yellow roses and onyx (the stone I tried to depict here) both have negative connotations. Yellow roses for jealousy, decrease of love, infidelity… and onyx for fear, sadness and similar fun things, but is also said to repel negativity and protect its wearer from the hostility of others. It is a gem thought to enhance determination and perseverance. And the dark color fits Sombra well.