Ryumaru, does look good, nice, clean, seems dark for some reason, I think you brought the darker colors towards the center, where as, I brought the lighter colors into the darker ones, interesting to see how it changes the contrast of the sphere. Anyway...
Ok, heres another excercise I thought up, 3 spheres, 3 light sources, only 4 colors though on each sphere, and the goal in this one is to not only smoothly dither the 3 spheres but to connect them with dithering using the blue background behind it, though it may look ugly, i thought it would be good practice.
good luck.