I carried out a quick test: it only appears to happen in my case (Roon 2, 1413 on macOS 13.6.7) when I’ve specifically marked an Album as having the Genre ‘Classical’.
Since all my Albums are what is commonly called ‘classical’ music, such a use of Genres makes no sense for me… rather, ‘classical’ refers to the era of music written (and not even necessarily performed) between, say, the birth of Haydn (1732)/death of Bach (1750) and the deaths of Beethoven (1827) and Schubert (1828).
I hope I may be forgiven for (I hope respectfully) waving a tiny little flag in the midst of overwhelming odds because I suggest that this means that few lovers of ‘classical’ music would use such a Genre in Roon in the way Tony suggests here - to evoke the (IMHO very attractive) parchment effect, which, FWIW, is the default ‘theme’ for the notation software, Sibelius.