Awesome work thus far, but I would suggest the following:

• Remove the white background fill behind the ring and, in fact, remove white entirely. The white in your design serves only to distract the eye away from the focal point and your characters. Replacing the white fill behind the ring with transparency (nothing) will make your design pop out against your t-shirt color choices. Additionally, fill in the white elements of the Chief's helmet with grey.
• Remove the blue eyes on the Chief. They're unnecessary and break the solid, iconic profile of the Chief's visor.
• This is very important! Keep the Chief's belt brown! It provides a nice splash of color in the focal point and solidifies the contrast of bright hues on the left of the image and dull grey on the right. The balance is pleasing.

Rough Mockup: