动态修改文本框更改中的不可数单元格

I have a table that creates new rows through PHP in regard to a database table that gets updated. Each row contains a unique class "rdClass" with an additional number that is incremented by a counter. A textbox is contained within each row with a unique id "workhr" with an additional number that is incremented as well. (rdClass0, ..., rdClass[n] ---------- workhr0, ..., workhr[n])

<td class='rdClass" . $counter . "'><input id='workhr" . $counter ."' name='HrsInShift" . $counter . "'></td>

What I'm trying to do is change the background color of rdClass# whenever the value in textbox workhr# changes respectively. I've already created a nice script in JQuery but it's not dynamic.

$(function() {

content = $('#workhr0').val();

$('#workhr0').keyup(function() { 
            if ($('#workhr0').val() != content) {
                content = $('#workhr0').val();
                $('.rdClass0').css("background-color", "blue");
            }
            else
                $('.rdClass0').css("background-color", "");
        });
});

How could I make this dynamic so that it detects value change for all workhr[n] and modify their rdClass[n] background colors respectively?

var dynamic_val;
$('[id^=workhr]').keyup(function(){
    if($(this).val() != dynamic_val){
        dynamic_val = $(this).val();
        $('.rdClass'+$(this).prop('id').split('workhr')[1]).css('background-color', 'blue');
    }else{
        $('.rdClass'+$(this).prop('id').split('workhr')[1]).css('background-color', 'inherit');
    }
});