The idea I'm trying to express is that the two are similar due to how different they are, or more to the point, similar in the details of the difference. If you take the two central aspects of their appearance (IE: structure and color), one went with the exact opposite of the other. "Contrast" doesn't quite swing it since that doesn't imply that the reversal is akin to an homage, and "Juxtaposition" doesn't seem to really swing it, either. And I'd prefer to not make up fruity terms like "counter-reference" or "diametrically balanced". The sort of thing that could be used to cover how Gulliver among the Lilliputians is, versus Gulliver among the Brobdingnagians is, you know? Or the sort of story where Character A has a particular relationship towards Character B at the start, but by the end, the roles are reversed so B is now that way towards A.
I'm at a loss for a simple, yet accurate, word/term to cover that palindromatic dichotomy.