When we were setting up the Christmas tree, I saw that a few of the balls were losing their paint, so I painted them :)
(The time span I filled in doesn't include the time for drying)
First, clean the balls.
Then spray paint them in the colour you like (I chose black).
Let dry and spray another layer if necessary. It is better to spray a few thin layers, than one thick layer.
When completely dry, take your gold paint and paint on any figures you want.
Now you can hang them in your tree! :)