The phrase "dark undertones" refers to hidden and often negative or disturbing aspects or feelings within something, such as a story, a situation, or a person's behavior. Full definition
The film itself has a remarkably dramatic edge to it, moreso than the previous films, with the buddy comedy peppering in dark undertones of adolescent trauma, the dullness of adult life, and the frustration inherent to drug abuse and depression. (alcohollywood.com)
Vibrantly colored flowers and ripe fruit are interwoven with dark undertones, mirroring the romantic and ethereal character's mysterious narratives. (spoke-art.com)
Some problems for Sonic Forces lie within its story, where Sonic Team has tried to play more on dark undertones than any other Sonic title. (seganerds.com)