Hi Callierae, it's hard to suggest a color without seeing the comforter, but here are some suggestions for kid's bedroom with blue walls.

This is his comforter, maybe this will help! Thank You

Since he's probably going to outgrow those dinosaur sheets in the next couple of years - I'd just select a nice medium blue tone that he likes.

Benjamin Moore Costa Rica Blue, Atlantis Blue and St Lucia Skies are great vibrant midrange colors that any boy would enjoy.

Thank You so very much!

Interesting. I would tend to pick softer blue colors such as the following from Benjamin Moore.

I have 3 sons and am an Interior Designer in Cincinnati, my favorite blues in a boys room are a dark denim blue such as Sherwin Williams 6249 Storm Cloud or if you like a lighter blue 6246 North Star. Blues tend to intensify greatly on the wall so you should choose a paint where the sample is much grayer than what you might think to select.