I really like the concept and you have unified design. I think the colors are fine minus the green ball under his foot. With only one ball, I'm not sure what its use is. Dose he use it to skate through the air somehow or something?
I believe the line art can be much cleaner and more dynamic. What I mean by dynamic is having more line weight. I believe Marc goes over this in one of his videos. Check this video out Also here is an image that can help as well.
When it comes to the rendering, I think the lighting is a bit weird. You seem to have this top left light and a blue top right light but there are areas that look a bit odd like the metal piece on the back of the jacket. You need to define the shape better.
Other things I believe you can work on:
Pose - The gesture doesn't flow well right now. The figure looks like its using a lot of 90 degree angles. Use more shapes to construct the body. Hopefully this video can help explain shape usage. Good reference for your case is to look at ice skaters since he is a wind spirit
Proportions and Anatomy - The head connecting to the body feels broken as well as the arms to the body. The bicep and triceps look to big for his body. The feet look odd as well. I also recommend changing to pose of the hands. Look at sprinters and again skaters. Look at reference. Draw the naked body underneath to make sure the anatomy works. Even if the rendering was good, if the anatomy and proportions aren't, it can lower the quality of the piece as a whole.
Rendering - Draw the body in a simpler form that is easier to add lights on to give yourself an better example of how to light your own character...This might not make since the way I wrote it but here's a tutorial video just in case. Seeing as it is a more cell shaded character, things can be a bit more simple. Studying others can help as well.
Now I do like the design the way it is but to enhance it I believe you can have the armor parts look more aerodynamic. Look at jets or sports cars. This will help him look like he can move fast while he rides the wind.
Hopefully this helps. If there is anything I missed then someone else might point it out. Hopefully this all makes sense and helps. If you have a question, hopefully I can answer it. Best of luck on everything.