The detail that best supports the analysis that “Character is who you are in the dark” applies to both "The Most Dangerous Game" and "Lather and Nothing Else" is:
The barber has been secretly helping the rebels.
This detail highlights the barber's hidden motivations and the complexity of his character, revealing that he has a secret life that contrasts with his public persona. Similarly, Rainsford's character is tested in the dark of the jungle, where he must confront his own morals and the consequences of his actions as a hunter. Both characters reveal their true selves when faced with challenging circumstances, illustrating the theme that character is defined by one’s choices in moments of darkness or crisis.