In one early strip, Krazy and [Ignatz] argue about the theory of evolution. Krazy is particularly taken with Darwin's idea "that we all sprang from the same source." Ignatz prefers the "polygeneric theory" that "you kats were always kats and we mouses always mouses." This argument between Krazy and Ignatz exactly mirrors post- Darwin debates over race, with virulent racists preferring the "polygeneric" theory that humanity does not share a common source.

In later strips, Krazy and the other characters would often switch between black and white with delightful abandon. In a 1931 strip, an art critic visits Coconino County (home of [George Herriman]'s imaginary animal kingdom) and describes Krazy and Ignatz as "a study in black & white." Krazy catches his meaning - "He means us Me bleck. You white" - and suggests to Ignatz that they "fool him. You be bleck and I'll be white."

We can see the racial comedy of passing played out in some of the strips. In the June 22, 1935, strip, Ignatz is blackened after hiding in a dirty pipe. Meanwhile, Krazy is thinking about her lover- mouse. "L'il blondish beautiful - so pink - so fair," Krazy sighs. Krazy is annoyed by the black-face Ignatz, mistaking him for "a l'll eethiopium mice." Only when Ignatz is washed clean does Krazy's happiness return.