I dont know but i just wanted to say you are too cute to be worrying about this. Your proposal will be perfect, and if you're worried about the box, just pull it out of your pocket sans box
I'm just one of those people who likes to have all their research and preparations made well in advance. Worried that a nonstandard ring box, say orange for example, will be more difficult to hide.
Are you planning on proposing right away after you receive your ring? If not, you can always search ebay or etsy for some used ring boxes that would be black/flatter/more inconspicuous!
I don't have any Gabriel & Co jewelry so no idea and I wasn't able to find any photos that I can be sure of as the box. With that said, I don't think the Gabriel and Co box is anything special. Maybe you can get a Faberge like case.
The jeweler who orders the ring usually will provide the ring box. Very few rings come with one from the maker unless it is luxury brand. And you pay a LOT for those boxes!