Most of us shade around the eye and head. It helps the eye look a little more natural. I usually shade down the spine as well. if that was my bait, I would add some black to the blue I was already using and shade with that. I don't like using straight black to shade. You can add a drop of black, paint one pass down the side, add a drop of black, etc to help fade the color to a darker blue.

When using a stencil try spraying on the edge of the stencil not directly on the lure...it creates a softer edge. Also, to stop paint spattering turn up the air and/or thin your paint a little more. When the paint doesn't atomize properly those are two remedies I've found that help. Use transparent colors for most situations then enhance the pattern with iridescent and pearlescent colors. In the case of pearlescent paints I've found that transparent over pearl can create some nice effects...easy on the transparent. Keep at it and find your own style...thanks for posting your work.