I took some “artistic liberty” here and avoided dithering altogether. My reason for this is because I felt that applying dithering to a sphere gives the false impression that the surface of the sphere is rough or pitted, like the surface for example of an orange (fruit - with small dimples on its surface).
Also, I deliberately avoided adding a reflective shadow in a crescent shape at the opposite edge of the highlight. I feel that adding such a reflective highlight somehow detracts from the main highlight, especially with graphics like these that are so small. Perhaps including or omitting the reflective highlight depends on the overall look and feel of the other graphics which would create a coherent consistent set of graphics within a single game.
To me though I was happy with the result without any dithering and without any reflective highlight.