We like for our 120/208 panels to have a crosshatch pattern, and the 277/480 panels to be solid...so do this:
Open your panel family - from the Family Types dialog, add a new parameter named Panel Voltage. Set this to the main voltage (120V or 277V).
Load the family into the project, then go to Visibility Graphics for the electrical view. Create a view filter that looks for a specific property of the panel, such as the Panel voltage parameter you made in the family - set it to look for an exact value that matches what you set in the family pick the 120v or 277v subcategory. Once you define the filter, add it the view - under the Patterns column, select override - make sure you check the box for visible, and then set the color and pattern you want to use so the equipment is "hatched". You might have to adjust the space of the pattern to get what you want, so make sure you duplicate an existing pattern and work from the duplicate.
later - David B.