This was actually an accidental upload. I put it on the upload page to see if the artist was already here, decided not to upload it and then began to work on another. Had the next one all tagged out and ready to go, hit submit, then this showed up. Turns out I forgot to clear the upload page and put the other post's source in.
I was immediately assuming British Jane Austen period, but then I remembered Swiss regiments of that time also had scarlet coats ( and perhaps were more likely to have black facings at a wild guess ). And also the Dano-Norwegian infantry.