The fill box on the left of the Color tab displays the fill color of the selected object(s). You can apply a color, pattern or gradient to the fill box. On the Fill tab of the panel, you can set the fill properties such as the Fill Rule or Transparency.
 
Fill Rules
You can choose between two fill rules: Even-Odd Fill or Winding Fill.
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Transparency
You can set transparency for any color that is selected or composed. This means that you are able to use transparency for that color in your design and ultimately on your prints.
Overprint
If you want to use overprint instead of trapping, you can activate overprint for a particular object by checking the Overprint box.