$arreglo = array(
    'color' => $skin['Color'],
    'textu' => $skin['ImagenTextura'],
    'header' => $skin['Imagen'],
    'sombra' => $skin['ImagenSombra'],
    'tooltip' => $skin['TooltipColor']
 );

echo json_encode($arreglo);

$.ajax({
            url: 'ajax.php',
            type:'POST',
            dataType : 'json',
            data: { 'dataString': result },
            beforeSend: function(){
                $("#loader").show();
            },
            success: function(output_string){
                            alert(output_string['color']);
                            }
      });

$.ajax({
    url: 'ajax.php',
    type: 'POST',
    dataType: 'json',
    data: {},
    beforeSend: function(){
        $("#loader").show();
    },
    success: function(output_string) {
        $.each(output_string, function (i, item) {
             alert(i + " " +item);
        });
    }
});