For this tutorial I will use a simple ball
with the ellipse tool and a dark blue filling
drag and drop your swatch over and into the ball
take the smudge tool and smudge the blue to
outside the circle with even strokes.
This will give you a natural blend of the blue
from the ball and the white background. The white
that blends will be your highlights.
Now we are going
to turn the image into a transparency image. This is
when the white will show up as a highlight. Click "Layer"
1. on the screenshot, then 2. transparency and 3.
alpha channel. Now grab your magic wand, indicated in
the screenshot. Hold the wand over the white and click.
Then hit your delet button or go to "clear." The
background will end up transparent and your white highlights
will be visible.
You can now put your image over a dark background
so the highlights really show up.
Remember to save your image as a PNG OR GIF, JPEG, does not
support transparency. Ok, Good luck!