Changing the background colour of a tabe cell, according to the selection in a drop down list

I have a drop-down list wrapped in a subform in a table cell. Users can pick Green, yellow or red and I want the background colour to change according to their selection.

Can you tell me why this script is not working? I am sure some of you folks can see it in a second.

if (this.ListItem=="green") {

Subform1.DropDownList1.fillColor = "000,128,000"; BackgroundFill="solid";

}                  

if (this. ListItem=="yellow") {

Subform1.DropDownList1.fillColor = "255,128,000";

}

if (this.ListItem=="red") {           

Subform1.DropDownList1.fillColor = "255,000,000";     

}

Thanks