Most likely with the paint
issue they will use a color gun to match the paint
color as best they can. They will paint
the repair and blend as best as they can. Old is old, new is new, they will never both look the same. It's up to you if you want to pay the difference to paint the rest of the bottom.
The insurance company is responsible to make you whole not better than whole so you're not likely to get the whole bottom painted on their dime.
After you get a firm cost of repair then approach the shop to paint the rest of the bottom to match. Personally I would pay the extra. And then paint it whatever color I wanted at that time. You will always have the memory of the accident but having to look at the bruise every time you walk near your trailer is more than what I would want. The other thing is, if you sell your trailer and disclose the accident, do you want to show them the bruised face or do you want to point out how wonderful the shop repaired it. A year after the extra money is spent you'll get over it and spend happy days exploring with your trailer.