alternating pattern in table

Hi,

Here is an explanation: Overprinting in InDesign (adobe.com)

Overprinting is a technique that allows you to set the color of one object to mix with any colors underneath. For instance, without overprinting, a yellow object placed over a blue background knocks out the blue and prints as yellow. But with overprinting turned on, the yellow object mixes with the blue background to create green.

In your case, it would be important if you had any design behing the table for example.