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 demonstrates that the barber's true character and moral decisions come into play when he is faced with the decision to kill Captain Torres or spare him. While he is known as a skilled barber, his actions in secret illustrate the complexity of his character and his values, which are revealed when he is placed in a morally challenging situation.
In "The Most Dangerous Game," a similar theme can be applied to Rainsford, especially when he is hunted and must confront his own values and ethics. The juxtaposition of his identity as a hunter versus his survival instincts under duress shows his true character when pushed to the limit.