How to format every secound row in a database result

Hi! I wish to format the output of a database select. The result is presented in a table, in which i'd like to present everey secound row with a different background color. My idea was to test if the remaining number of rows where a prime number or not, and by that determent if the background color should be white or som ivory-like color to improve the readability in the result table... Hope to hear from anyone with experience in similar matters... TIA! Georg Herland, Norway