As you loops through your data, you need to determine if a given row contains the "OCOMsg2" field you're looking for, and if it does write out the following:

<tr style="color: red;">
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Otherwise, just write out a plain tr tag with no style attribute. You need to do this before splitting the row into individual parts - or else use join to put them back together in order to do the check. Something like this:

use strict;

my @stat_array = (
"ibfarm102  - localtick", 
"Boston" , 
"hibmis100 -  procHKHD2 - Hongkong", 
"PidMonRsp", 

"eufarm102  - localtick", 
"London", 
"hibmis100 -  procHKHD2 - Hongkong", 
"PidMonReq", 

"ibfarm102  - localtick", 
"New York", 
"hibmis100 -  procHKHD2 - Hongkong", 
"PidMonRsp", 

"ibfarm102  - localtick", 
"New York", 
"hibmis100 -  procHKHD2 - Hongkong", 
"OCOMsg2"
); 

while (my @group_of_4 = splice(@stat_array, 0 , 4)) {

  my $rowstring = join(' ', @group_of_4);
  
  if ($rowstring =~ /OCOMsg2/) {
    print  MAIL "<tr style=\"color: red;\">\n";
  } else {
    print  MAIL "<tr>\n";
  }

  for my $data (@group_of_4) {
    print MAIL "<td>$data</td>\n";
  }
   
  print MAIL "</tr>\n";
  
}
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I get this output:

<tr>
<td>ibfarm102  - localtick</td>
<td>Boston</td>
<td>hibmis100 -  procHKHD2 - Hongkong</td>
<td>PidMonRsp</td>
</tr>
<tr>
<td>eufarm102  - localtick</td>
<td>London</td>
<td>hibmis100 -  procHKHD2 - Hongkong</td>
<td>PidMonReq</td>
</tr>
<tr>
<td>ibfarm102  - localtick</td>
<td>New York</td>
<td>hibmis100 -  procHKHD2 - Hongkong</td>
<td>PidMonRsp</td>
</tr>
<tr style="color: red;">
<td>ibfarm102  - localtick</td>
<td>New York</td>
<td>hibmis100 -  procHKHD2 - Hongkong</td>
<td>OCOMsg2</td>
</tr>
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If that's not what you want - hopefully it's enough to get you going in the right direction.