It was named "Chapi Chapo" as a play-on-words with the French word, chapeaux, which means "hats". Both of the main characters wore oversized hats that matched their clothing. In the theme song they say, in French:
"Guess who is Chapi.
Guess who is Chapo.
Who of us is Chapi, Chapo.
That is entirely in red Chapi.
The blue is Chapo.
But we are like twins..." (rough translation)
So, the one in red is Chapi and the one in blue is Chapo.