case sensitivity.
on the success page, you have the following to write the size and color:
<td class="eC_GroupColumn"><?php echo $eCart1->DisplayInfo("size"); ?></td>
<td class="eC_GroupColumn"><?php echo $eCart1->DisplayInfo("color"); ?></td>
in the email though, you use upper case for the first letter of size and color:
$MailBody = $MailBody . $eCart1->DisplayInfo("Size");
$MailBody = $MailBody . $eCart1->DisplayInfo("Color");
change those 2 lines to use the same case as you have on the success page.