Visto che forse non mi sono spiegato bene, ecco il codice in oggetto:

Codice PHP:
<table border="0" cellpadding="0" cellspacing="0">
        <tbody>
          <tr>
            <td width="220" height="24" class="testo_normale_space_white">Collaboratore</td>
            <td id="border_gray_verticale"></td>
            <td width="50" align="center" valign="middle" class="testo_normale_center_white">Turno</td>
            <td id="border_gray_verticale"></td>
            <td width="150" class="testo_normale_space_white">Informazioni</td>
          </tr>
          <?php
        $y = 1;
         do {
                $colorRow1 = "";
                         if($y % 2 == 0){
                              $colorRow1 = "riga_pari";
                         } else {
                              $colorRow1 = "riga_dispari";
                 }         
            ?>
          <tr>
            <td colspan="6" id="border_gray_orizzontale"></td>
          </tr>
          <tr>
            <?php $explodeColor = explode("|", $rs_get_personal_daily['Color']);?>
            <td height="24" id="<?php echo $colorRow1;?>" class="testo_normale_space"><?php echo $rs_get_personal_daily['LastName']." ".$rs_get_personal_daily['FirstName'];?></td>
            <td width="1" bgcolor="#D3D3D3"></td>
            <td <?php if($rs_get_personal_daily['Color'] == NULL) {?>id="<?php echo $colorRow1;?>"<?php } else {?>bgcolor="<?php echo rgb2hex($explodeColor[0],$explodeColor[1],$explodeColor[2]);?>"<?php }?> class="testo_normale_center"><?php echo $rs_get_personal_daily['TaskKey'];?></td>
            <td width="1" bgcolor="#D3D3D3"></td>
            <td class="testo_normale_space" id="<?php echo $colorRow1;?>"><?php echo $rs_get_personal_daily['TaskName'];?></td>
          </tr>
          <?php
        $y++;
         } while ($rs_get_personal_daily = sqlsrv_fetch_array($sql_get_personal_daily))?>
        </tbody>
      </table>
In pratica quando cambia il valore di $rs_get_personal_daily['TaskKey'] deve comparire una riga rossa di separazione.

Spero che sono riuscito ad essere più chiaro

Grazie per le risposte che mi avete già dato