Kamon is the childish counter culture view of adulthood. He is a kid in an adults body. He has discovered sex but doesn't quite get how one gets it by being mature. He helps create a sort of love triangle between himself, Haruko, and Naota.
FLCL is a coming of age story. German has a much cooler word for it, bildungsroman. To understand Kamon better you must understand his level of balance and where it lies in relation to other characters. By going by balance we can add Atomsk because when the two extremes meet (Naota and Canti) we get Atomsk.
From least adult to most we have Naota, Kamon, Atomsk, Amarao, and Canti.
Naota is an extreme character, going from loud to very quite and having very defined tastes and preferences. He is very childish and while he thinks he is more adult than the actual adults around him it only shows how much more of a child he is. Kamon is mature but usually very childish. He never goes overboard with it like Naota does. He knows what he wants which is very adult but uses childlike methods to get them. For example he fights with his own son for Haruko. Atomsk is what everyone strives to be like. Naota and Canti together can achieve this balance but people like Amarao can't. Speaking of Amarao, he is rather childish but also strives to be an adult. He sees adult things and tries to emulate them. Amarao strives for the balance that Atomsk displays but fails in achieving it because he is too extreme. Canti is a servant: he is humble, kind, outgoing, and easy to get along with to name a few. He is the most adult and shows no childish behaviors.
Kamons parenting style is very lax. He guides Naota but understand that for anyone to truly learn they must safely experience life for themselves. This is what makes him so mature. Everything else about him though displays childishness.
If his head was good for opening N.O. channels Kamon has the ability to balance himself out the way Atomsk is. Kamon can be rather adult but chooses not to. Haruko would have probably preferred Kamon because of these traits. We have seen Kamon changing colors already. In both his clothes and his skin. It wouldn't be too hard for him to bring out Atomsk.