I recently found a clear color image of the trombone-playing cherub in Milan’s San Simpliciano. I have replaced the old, blurry, black and white image in the Trombone History Timeline (16th century) and in the HubPages article, Trombone History: Cherubs Playing the Trombone (where you can view 10 additional depictions of cherub-trombonists). An interesting side note: the cherub to the right of the trombonist may actually be playing a serpent; if so, it would be a very early visual depiction of the instrument.
You can see the new image, along with its caption, immediately below. Beneath that are two additional views of the painting. Enjoy!
c. 1590—Milan, Italy: Aurelio Luini depicts a cherub playing trombone in his fresco in Milan’s San Simpliciano (see below image; public domain) (Kendrick, Sounds of Milan 77 [black & white version]).
Here is a view of the full cherub painting (click image for larger version):