Alternate colors (background) titlebox Ajax portfolio

Dear Enfold crew,

to differentiate, I try to use a cool new css function to give some extra dynamics to my site.

Basically I would like the title box background in Ajax portfolio, to be different every second portfolio item in an overview like this:

http://kriesi.at/themes/enfold/portfolio/portfolio-ajax/

Then, here comes the css I found on this page; http://amethystwebsitedesign.com/alternate-colors-in-post-and-widget-titles-with-css-nth-of-type/

With this css, every second post (2n) starting on 2 (2n2), so 2, 4, 6, 8, etc.. is given it’s own color using

.post:nth-of-type(2n+2) .entry-title a {
	color: #046ca3; /* dark blue */
}

My problem is that I cannot find the container class where this background is in, so I can copy it to my child css and create the code. I have come as far as this:

#blocks .grid-content {
	background-color: red;
}

#blocks .grid-entry-title  {
	background-color: red;
}

This changes the color, but if I insert

#blocks .grid-content:nth-of-type(2n+2) {
	background-color: red;
}

#blocks .grid-entry-title:nth-of-type(2n+2)  {
	background-color: red;
}

it does not work. I got the feeling i’m not addressing the right container, so I was hoping you guy’s could help me pointing that out. So I’m looking for the right class to adress, in order to make nth-of-type effectively work.

Looking forward, thanks, Daniël