Highlighting column results based on MYSQL value

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PHP

MySQL

SELECT *
FROM emp
WHERE NOT EXISTS (SELECT emp_old.roll_no, emp_old.name
FROM emp_old
WHERE emp_old.roll_no = emp.roll_no AND
emp_old.name = emp.name)

Above query works and selects unmatched columns of roll_no & name but the results is comming combined of this 2 conditions i need to highlight which roll_no is not matched & which name is not matched..
i had tried as follows but if i insert color it shows for whole column i need for wrong data only..

while($row=mysql_fetch_array($res)) {
echo ""; echo "" . $row['roll_no'] . "";// which rollno is wrong in red color
echo "" . $row['name'] . "";//which name is wrong in blue color
echo ""; }