Tip on writing in the future, Try not to use -ette with anything but words it already existed with.

To other authors/readers, it may seem lazy or immediately will make readers/authors sigh or roll their eyes.

(I'm not sending hate, I'm genuinely trying to help since I see a lot of other authors get made fun of or just hated on for doing certain things like this,  and as a person who is aiming to be a professional author these are just some tips I've learned along the way.

Again no hate, I just want to help avoid you being made fun of or authors/readers thinking you're cringy/not taking you seriously or thinking that you are a troll/ a joke)

To give an example here is your sentence, which is really
"He was sitting in a child's seat on a rolling cart, staring at the greenette"

Again Try to avoid using -ette in any word it was not originally paired with. 
Instead, try this:

"He was sitting in a child's seat on a rolling cart, staring at the *Insert word that describes the shade of color* green haired boy."



Or alternatively, "There was a young boy, seemingly about Izuku's age,  staring at the messy green haired boy" 

I am also not a professional author, but what I've learned from other authors is to try and avoid using ette unless it's already paired with that word, ex: brunette.

No hate, this is really good, I'm just trying to help.