This is, indeed, a painting by Joseph Solman. Gouache is known for being one of the more opaque paints out there, but the transparent feel could be created by adding water to the paint so that the newspaper underneath could be seen slightly. The picture does give off a hazy feel, but even before reading the fourth statement, my eyes were immediately drawn (no pun intended) to the thickness of the lines and how it contrasts with the lighter, less saturated pigments in the painting.
So, you can see that I pretty much agree with all of these statements, except for the third. It doesn’t really make that much sense to me, since portraits are typically of the person looking at the front of the person, not of their back. Whilst doing research, I was unable to find a picture of what Solman looked like when he was younger, so I was unable to tell if the person in the painting and Solman had any kind of resemblance to one another. What really sells it for me is the fact that this piece is called Red Hair, which isn’t something I would imagine someone would call a self portrait.
Hope this helped you out! Feel free to ask me any additional questions if you have any. 🙂