Finding incorrectly marked rows for overdue books

Rows in red are supposed to represent overdue books.

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.3.3/semantic.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.3.3/semantic.js"></script>
<table class="ui table unstackable firstTable"><tbody>
    <tr style="background-color: red">
        <td>Donna</td>
        <td>2016-10-01</td>
        <td></td>
    </tr>
    <tr style="background-color: red">
        <td>Nansen</td>
        <td>2016-11-05</td>
        <td>2016-11-14</td>
    </tr>
    <tr style="background-color: red">
        <td>Peppe</td>
        <td>2016-11-05</td>
        <td>2016-11-14</td>
    </tr>
    <tr>
        <td>J'Sira</td>
        <td>2012-02-28</td>
        <td>2012-03-14</td>
    </tr>
    <tr>
        <td>Billie</td>
        <td>2015-08-14</td>
        <td>2015-10-09</td>
    </tr>
    <tr>
        <td>Peyton</td>
        <td>2015-08-14</td>
        <td>2015-10-09</td>
    </tr>
</tbody></table>

<br><br>

<table class="ui table unstackable secondTable"><tbody>
    <tr>
        <td>Addison</td>
        <td>2014-08-14</td>
        <td>2014-10-09</td>
    </tr>
    <tr>
        <td>Val</td>
        <td>2014-08-14</td>
        <td>2014-10-09</td>
    </tr>
    <tr>
        <td>Patrick</td>
        <td>2015-11-23</td>
        <td></td>
    </tr>
</tbody></table>

JavaScript

function solution(D, T, whichTable) {
	var table = $('table.' + whichTable), // REMOVE .this FOR TASK
  		howManyMarkedIncorrectly = 0;
		
	table.find('tr').each(function() { // Search through each table row
  	var This = $(this),
        dateBorrowed = new Date(This.children('td:nth-child(2)').text()),
        dateReturned = This.children('td:nth-child(3)').text();
    if (dateReturned) { // Check if book was returned
    		dateReturned = new Date(dateReturned);
    }
    var currentDate = new Date(D),
        daysAllowedToHoldBook = T,
        diff_fromCurrentDate  = new Date(currentDate - dateBorrowed),
        diff_fromReturnedDate  = new Date(dateReturned - dateBorrowed),
        overdue = false,
        markedRed = false,
        markedIncorrectly = false;
    
    // Check if book was/is overdue
    if (!dateReturned &&
    		convertIntoDays(diff_fromCurrentDate) > daysAllowedToHoldBook ||
      	convertIntoDays(diff_fromReturnedDate) > daysAllowedToHoldBook) {
          overdue = true;
    }
    // Check if row was marked Red
    if (This.css('background-color') == 'rgb(255, 0, 0)') {
          markedRed = true;
    }
    // Check if row was marked correctly with/without Red
    if (!overdue && markedRed ||
    		overdue && !markedRed) {
          markedIncorrectly = true;
          howManyMarkedIncorrectly++;
    }
  });

  function convertIntoDays(num) {
    return num/1000/60/60/24;
  }

	return howManyMarkedIncorrectly;
}

console.log(solution('2016-11-30', 14, 'firstTable'));
console.log(solution('2015-11-30', 7, 'secondTable'));