Ok. I will update my own post.
After creating the fields if you go back and set a fill then set it back to none and save the changes it will retain the fill option of none.
I guess I just do not expect anything to change in a custom style after I have saved it. It appears FileMaker is only saving the css for the items I changed from the default.
This does make sense in a pure css world but since we can not view the detailed css per style; I think a better behavior is to copy the css entirely. This would ensure custom styles would not get updated unexpectedly. Otherwise giving us access to view the css would make it easier to see what will be changed when overriding the default. As it stands it is impossible to know which objects will be changed.