Camaleónica literally means "chameleon-like" or "chameleonic." It's an interesting and less common adjective that paints a vivid picture.
In the song, it's used to describe the lover as "camaleónica de artes escénicas" (chameleon-like in performing arts). This suggests she is adaptable, mysterious, and perhaps changes her persona, adding to her allure and the secretive nature of their relationship.
"Invisibles" is about a relationship the singer keeps hidden from everyone around him. The hook repeats the idea that he and this person only kiss and see each other where nobody can see them, so as far as the outside world knows, they don't exist as a couple.
The verses fill in why the secrecy matters more than being seen: he doesn't want people talking, and even though he knows the truth would come out eventually, he says it barely bothers him. He mixes blunt, physical lines about being close to her with softer ones about how much he values having her by his side and how she's saved him more than once. By the end he decides that staying invisible together is worth it, as long as what they have stays real.