When I have a value as an empty string "" in the data and I use background color in cellTemplate it does not color enitire cell. Here is the plunke that illustrates the issue.
http://plnkr.co/edit/TP4VH9xA7qCFT8xgNKW8?p=preview
Can someone help me fix it.
I found a workaround, in cellTemplate you can check for an empty/null string and add the HTML  
(non breaking space) entity, this way your cell will be properly rendered.
Example:
cellTemplate: '<div class="yellow" ><div class="ngCellText">{{row.getProperty(col.field)||" "}}</div></div>'
Changed your plunker, here's a working example : http://plnkr.co/edit/tR6UKCrXZqKi5HwsWOAV?p=preview