The Sparkles Effect creates an image of stars where the intensity and concentration of stars depends on the original image: You can change:
The dialog looks like this:
The variability slider sets how much the size and color of the sparkles changes within the image. To keep the effect of a sparkle the color variation is only applied to the outer color, while the inner color (usually white or a very light color) is not affected by the Variability setting.
To get an effect with many different colors in the sparkles you should put the outer color to a strong color (not white) and then set the variability to 1.
Increasing the image quality (IQ icon 
) can be effective with the Sparkles. You can image mixing too. See also the Stardust Effect. and the Snowflakes Effect.
