php 相同的产品 一个背景色

Array
(
    [0] => 12
    [1] => 17
    [2] => 17
    [3] => 17
    [4] => 17
    [5] => 3
    [6] => 3
    [7] => 3
    [8] => 3
    [9] => 3
)
Array
(
    [0] => 12
    [4] => 17
    [9] => 3
)
Array
(
    [12] => 2
    [17] => 1
    [3] => 2
)

$i = 0;
                            foreach ($arr as $key => $value){
                                $i++;
                                echo $i;
                                
                                if($i%2==0){
                                $c = "1";
                                }else{
                                $c = "2";
                                } 
                                
                                
                                $c1[$value] = $c;
                                //$c1[‘class‘] = $c;
                                //$c2[] = $c1;
                                
                                //echo $value.$c."<br>";
                            }
                            
                            echo "<pre>";
                            print_r ($c1);
                            echo "</pre>";

<style>
                                .a1{background-color:#FFFFFF}
                                .a2{background-color:#FCF4F0}
                                </style>
                            
                            
                                <tr class="<?php echo "a".$c1[$bv[‘sid‘]];?>">