A very simple ornament to decorate and make your own. 
materials:
clear glass or plastic sphere ornaments
acrylic craft paints in an assortment of colors
small paper cups

Pour a little paint in a paper cup, add an equal amount of water, mix. Pinch the rim of the cup to form a spout.
Do for each color of paint you are using.
Remove the top of the ornament, be careful not to break the ornament if it is glass.
Pour a little paint of one color into the ornament, rotate it so the paint makes trails inside. Add another color, rotate again, repeat if you desire. 
"Less is more" applies here; two colors can be striking, four colors can be too much and muddy.
It is nice to leave some parts unpainted, so that light shines through.
Turn the ornament up side down, on top of a cup, and let excess paint drip out. Leave for a while.
Replace the top of the ornament carefully
Enjoy.