Evertrue discussion

Has anyone else noticed that the eye color of the characters… change?
In the very first pages of Everneath, Cole is described as a blond guy with dark eyes:

“His blond hair framed his dark eyes-eyes that were wide open now, in surprise.”

There are also some other lines that describe him as dark-eyed. Then, in Evertrue there’s a line about Cole that says:

“Clear blue eyes locked with mine(…)”

So, Cole’s eyes change color with no apparent reason.
The same thing happens with Nikki. She never describes herself, but in the novella from Cole POV, he describes Nikki:

“The one with dark-brown hair, side-swept over one shoulder, hanging in soft curls to her chest. Giant brown eyes, big as whole notes of sheet music.”

And then in Evertrue Jack says to Nikki:

“It’s the same green as your eyes”

So what’s going on? Could it be possible that it's mistake of the author? I think it's improbable -as the author, Brodi Ashton must know what the characters of her series look like very well- but I have no other ideas why there are these contradictory lines... Any ideas?