Colin,
>Excuse my ignorance but how do I add a method to a grid?
To add the method to the grid requires you to use a subclass, you could provide an abstract method like MyRowColoring() and then at the instance level of the grid on the form put code in the method and reference it in the DynamicBackColor properties.
If you don't need to use this sort of feature a lot, you could add the method to the form and reference that via thisform. in the DynamicBackColor property.