A lot of gay leather culture takes references from the military and motorcycle culture, and uniforms are no exception. As there are standards for the classic Leather Woman, so is there for the Leathergirl.
There is no strict guideline when it comes to formal wear for the leathergirl. If collared, refer to what your Dominate has declared. Otherwise, take the bar uniform and perhaps, ‘class it up’ a little. A few examples would be wearing a darker more fitted pair of blue jeans rather than your blue jeans for the bar, or replace the t-shirt with a button up and a leather tie, with a clean black leather vest that can fasten close. Have a ‘dress’ leather pair of boots that are high shine leather as opposed to oil tan leather.
Eventually in your Leather Journey, you will have a combination of either purchased or earned leather garments that allows you to dress from head to toe in full leather, also known as ‘full cow’. This will easily be considered, and most likely preferred, as formal wear.