Stackoverflow questions
HTML
<ul>
<li>First</li>
<li>Second</li>
<li>Third</li>
<li>Fourth</li>
<li>Fifth</li>
<li>Sixth</li>
<li>Seventh</li>
<li>Eighth</li>
<li>Nineth</li>
</ul>
CSS
ul > li:nth-child(3n+1){
/*whatever your property may be*/
background-color:orange;
}
ul > li:nth-child(3n+2){
background-color:white;
}
ul >li:nth-child(3n){
background-color:green;
}