css selectors - CSS nth-child apply odd-even rule but switch every 4 items

Question

I have a list of divs that appear 4 in a row with a class and I would like to create a checkerboard background style, meaning:

• Apply a different background color for odd and even divs
• Switch the odd-even to even-odd for each line

I've tried this

.boxwrapper:nth-child(2n-1), .boxwrapper:nth-child(2n) {
    background:#ff0000;
}
.boxwrapper:nth-child(4n-2), .boxwrapper:nth-child(4n-3) {
    background:#0000ff;
}

and it works fine for odd-even divs but cant get it to switch every 4 items. I'm headaching over the 4n-1, 4n+1 stuff, if I could get that right voila!

The result should look like this:

Answer 1

Demo

http://jsfiddle.net/mykhA/1/

HTML

<div class="container">
    <div class="box"></div><div class="box"></div><div class="box"></div><div class="box"></div>
    <div class="box"></div><div class="box"></div><div class="box"></div><div class="box"></div>
    <div class="box"></div><div class="box"></div><div class="box"></div><div class="box"></div>
    <div class="box"></div><div class="box"></div><div class="box"></div><div class="box"></div>
</div>?

CSS

.container {
    width: 100px;
    height: 100px;
}

.line {
    width: 100px;
    height: 25px;
}

.box {
    width: 25px;
    height: 25px;
    float: left;
}

.box:nth-child(8n+2) {
    background-color: red;
}

.box:nth-child(8n+4) {
    background-color: red;
}
.box:nth-child(8n+5) {
    background-color: red;
}

.box:nth-child(8n+7) {
    background-color: red;
}

.box:nth-child(8n+1) {
    background-color: blue;
}

.box:nth-child(8n+3) {
    background-color: blue;
}

.box:nth-child(8n+6) {
    background-color: blue;
}

.box:nth-child(8n) {
    background-color: blue;
}
?

?