jQuery Grid Plugin - jqGrid

A php script buids a list and the grid uses it like this:

var items= $.ajax(
    {
        url:'listofitems.php',
        async:false
    }).responseText;

The returned string has this structure:

"item1:item1;item2:item2;…itemn:itemn"

The column is defined like this:

{
        name:'reference',
        index:'reference',
        edittype:'select',
        editoptions:{value:items},
        editable:true 

 },

When the edit form is displayed I would like to see, for example, the odd items in red, the other ones in blue.

1) is it possible to "integrate" the color or the criteria in my script ?

2) and test in beforeshowform

Another solution is welcomed …