Place your ornament in a washi tape roll for stability.  Remove the top and set aside.

Pour a small amount of one of your colored paints into the ball. Note:  It is best to work with lighter colors, such as reds, oranges and yellows.  Darker colors such as purples and greens can make your finished ball look muddy.  Depending on yor paints you may also find that you need to thin the paint slightly to make it pour easily.

Add a few more colors of your choice.  Place your cork in the top of the ball.  Shake the ball to distribute the paint.  You can also spin the ball like a top.

Continue shaking or spinning until the entire inside of the ball is covered.  

Allow the paint to dry for an hour or so, resting on the washi tape roll.  Replace the hanger top.  All done.