Synonyms that are in the dictionary are marked in green. Synonyms that are not in the dictionary are marked in red.
Antonyms that are in the dictionary are marked in green. Antonyms that are not in the dictionary are marked in red.
While D-Con is right about the association of blue with both characters, Leonardo and Sonic are also similar because of the action-packed adventures they've gone on.
Source: https://screenrant.com/teenage-mutant-ninja-turtles-sonic-crossover-fan-art/