mainc character's name was Blue, there were fairies [s]

[Bryn]

I read this book in early middle school but i remember it wasn't a new release (pre 2000s), and it was for older readers.
The author was male, if I'm correct.
It was fantasy and it was a series.
It wasn't historical perse, but i thinkthe boy went into the fairy world, so it was more medieval.
There were two main characters: a boy who was human and a girl named Blue i don't think it was her real name but that's what everyone called her.

[Mo]

Was it Fairie Wars by Herbie Brennan?

[Bryn]

It was! oh my gosh thank you so much!

[Mo]

You're welcome! :)