I think you both were on the right track earlier.
One best practice I have employeed is to use visual inheritance.
In MM.NET this means, in the example of a winform, creating a new form within my application project that itself inherits from mmBusinessForm in order to have MM.NET capabilites.
It is on this new form, lets call it mmAppForm, that I can configure settings that I'd like standardized throughout the application. I personally have navigation buttons and shadow blending backgrounds that I use so I configure my mmAppForm to have those things.
Then, when I am ready to setup a CustomerForm, I inherit from my mmAppForm rather than the mmBusinessForm.

Another cool thing about this is that you application can permit user level customization which is then used through the application. This is done by simply progamatically taking the user selections and progamatically altering the mmAppForm. Remember it is this form that is the new base form for all the apps forms and so these changes will effect the entire application.

I do agree with Victor that for simple things like background color changes this would be better in configuration files as they are easier to work with for these types of things, but sometimes you have complex visual inheritance needs that config files cannot be useful.