Instead of manually painting in the transparency, I instead made two black/white gradients, which made the transparency change as you moved around the sphere (ignore the blue lines, they're just rulers I used to snap things to the center without overlapping).
I also used an orange/red gradient for the color instead of making it a solid color, and then duplicated it four times and rotated it (similar to the transparency gradient) so that it didn't abruptly switch to another color.