Listen...I get the whole wanting to replicate the Atari 2600 graphics style and such, but the whole characters lacking outlines thing really isn't that appealing to the eye. They end up blending in with the background and anything else even remotely close to their colors. Even now, your sprites are blending in with the VGR forum theme. I'd suggest giving them an outline of some kind, even if it's not some type of black.
Also, you can still have hue-shifted shading, even if your shading is only a single level deep to make the sprites look better.
Also, you can still have hue-shifted shading, even if your shading is only a single level deep to make the sprites look better.