I extended the DGColumn and added a "alternatingItemColors" style it so that it would be possible to set it per column.
I extended the DGItemRenderer and used the background and backgroundColor properties to set the items background color. I added logic in a overridden validateNow function to pick up the color from the alternatingItemColors color array.
The drawback of this approach is that the selection feedback gets almost hidden by the background coloring which would not be the case if the drawRowBackground function is overridden.
The result :
The source is available here.