For context, I am writing a graphic novel. I always used to imagine I would have some characters (mainly protagonists) reveal their internal monologue while others (mainly the antagonists) don't. They just express themselves with speech/actions. I wanted to do this for a number of reasons, one being I wanted some character's intentions to be hidden for awhile. I then realized this might seem like favoritism of certain characters and lead to the story seeming more black-and-white.
I thought one way to combat this (to an extent) is to allow all characters to reveal internal monologue, but some reveal all of theirs while others reveal less to varying degrees (maybe on a situational basis, such as only when they alone in their room).
I worry though that readers might get frustrated or confused by the inconsistency.
Is that something I should actually be concerned about or not? If so, what would you recommend I do instead? If you disagree about what I said regarding favoritism, let me know as well.