Compare, Flash file displaying spheres (above) 403 bytes. Icon displaying preview of Spheres (below) 4.13 KBytes.
This is a good example of why vector graphics are useful for displaying graphics over the web using a minimal amount of bandwidth.
To produce the effect I used a circle with a circular gradient, then used flash colour filters to recolour the movie clips by adjusting the hue and saturation. The grey ball at the back has had its brightness/contrast adjusted - but they all source from the same symbol in the library.