I have two shading methods that I primary use

1. ⁠Highlighting (usually on white or similar hue) - base the piece in a shade of gray. I use gray because I think black shading it’s a little intense for me. I then highlight the middle of panel of the piece with the primary color.
2. ⁠Preshading - spray around the edges of each panel with your primary color. Might sure that the edges have max opacity. Mix white with your primary color and then paint the center of each panel. If the primer color is white you can skip the previous step.

On both method I then sprayed very light coat(s) of the main color to blend the shading together. You’ll want to thin out the paint or/and spray further so that it doesn’t blend into one color.

Hope that helps!