The saying means what is considered good is in fact bad and what is considered bad is actually good.
an example could be you trust someone and they seem to be a good person but looks are deceiving and they turn out to be bad
Although we as the readers see how furious and proud of their beliefs both factions are, we see that they are arguing over something that is the same thing. Similar to arguing whether zebras are white with black stripes or black with white stripes.
I need the passage to answer this question
