The sphere element shows odd artifacts when being rendered semi-transparently. A Screenshot and example program attached (the program simply displays a blended sphere).

It looks like the sphere model incorrectly includes internal rings - the vertical lines.

It also looks like the order of the vertexes being drawn is effecting the final result. I believe in the screenshot attached, the darker left half is being drawn first, clipping out the back face of the model, while drawing winds around to the back of the right side first, resulting in the back and front of the model being rendered and leading to the lighter appearance.