We are going to make the following three glass balls Click on the image to jump to the tutorial you want to start with. Open a new image. I am using an image 200x200 with a white background.
Flood fill with any color.
Select your fill tool, with a radial gradient. Set your foreground color to the color you want to use and the background color to black. The black edges are where I ended my circle. Fill with the gradient. Your image should look like the following image.