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I am not sure if I have understood your question correctly.
Do you mean to say that you want to change the background color so that alternate row of form is displayed in the same color?
Please explain your requirement a bit more in detail and we will surely help you. You may also like to share a screenshot as well on how you want your form to look or where you want the changes to appear. The following guide should help you how to upload image in forum post: http://www.jotform.com/answers/277033
We will wait for your response.