cfgrid change cell color

After an exhaustive search for a solution, what I have come up with isn't working as the cell color isn't changing color. The alerts are alerting as expeted and correctly. Anyone have a clue what might be wrong?

formatStatus = function(data,cell,record,row,col,store) {                      
    statusValue = record.get('NAME_STATUS').trim();
    TDPcountValue = record.get('TDPCOUNT'); 

    if (statusValue == 'TDP REQUESTED') {

        if (TDPcountValue > 44) {                          
            alert('Red Status: '+statusValue+' Count: '+TDPcountValue);
            cell.css = '45Days';
        }       
        else if (TDPcountValue < 30) {
            alert('Okay: '+statusValue+' Count: '+TDPcountValue);
            }
        else {
            alert('Yellow Status: '+statusValue+' Count: '+TDPcountValue);
            cell.css = '30Days';
        } 
    }

return statusValue; 
}         

formatCells = function() {
    theGrid = ColdFusion.Grid.getGridObject('requestGrid');
    cm = theGrid.getColumnModel();
    cm.setRenderer(10,formatStatus);
}

<style>

.30Days {
background:#FFFF00; !Important
}
.45Days {
background:#FF00000; !Important
}
</style>

<cfset ajaxOnLoad("formatCells")>

Any help in the right direction would be great, thanks in advance!!

formatStatus = function(data,cell,record,row,col,store) {                      
    statusValue = record.get('NAME_STATUS').trim();
    TDPcountValue = record.get('TDPCOUNT'); 

    if (statusValue == 'TDP REQUESTED') {

        if (TDPcountValue > 29 && TDPcountValue < 45) {
            cell.attr += 'style="background-color:yellow;"';
            //alert('Yellow Status: '+statusValue+' Count: '+TDPcountValue);
            }
        else if (TDPcountValue > 44) {                          
            //alert('Red Status: '+statusValue+' Count: '+TDPcountValue);
            cell.attr += 'style="background-color:red;color:white;"';
        }           
        else if (TDPcountValue < 30) {
            //alert('Okay: '+statusValue+' Count: '+TDPcountValue);
        } 
    }

return statusValue; 
}         

formatCells = function() {
    theGrid = ColdFusion.Grid.getGridObject('requestGrid');
    cm = theGrid.getColumnModel();
    cm.setRenderer(10,formatStatus);
}

It seems that 'cell.attr' was the trick I needed instead of cell.css. Thanks to all for helping.