Intermediate Level Children's Chapter Book from 2000-2015ish with a Made Up Word for a Title

[Mariah]

So my friend and I have spent hours trying to find this book and this is our last hope.
She remembers this book that she read probably around 2008-2012, she doesn't remember much about the book accept for one part. In the part she remembers it talks about they specks of color you see when you close your eyes being how much creativity or imagination and person has. There is another part that she remembers vaguely about a person walking through a tunnel or a cave and having to be very quiet because there was a monster of some sorts in it. The cover was black with big white words but the title was like some made up word on multiple lines.
She rented from her elementary school library, but says it was probably a middle reading level. It did have pictures but it was a chapter book.
This is super vague and not a good description but this is all she remembers about it and we have been searching desperately everywhere we can think of to find it but have been unsuccessful this far.

[Rainbowheart]

Skellig?

[Kris]

Here's the Google Books preview of Skellig by David Almond - Rainbowheart's suggestion:

https://books.google.com/books?id=rRr... There are different cover images.