Arching, of the top especially, does affect the sound of a violin. Higher arched instruments – Stainers and Amatis for example – have a “silker, smoother” but often less powerful sound. Stradivari violins typically have a lower arching leading to a more powerful sound. The idea here is that a object that is flatter vibrates easier or more that an arched object since arching provides a bit of a brace that resists vibration. I believe that Guarneri violin usually have a lower arching as well, hence their power comparable to that of Strads. Since (or better, “if”) Strads and Guarneri violins have similar (lower) arching, this wouldn’t explain dark vs bright differences.
I’ve heard it said that violins with uneven arching — be it low or high — tend to have a thin, nasal sound. The aim is to have smooth, graceful slopes to the arches.
F-holes also influence the sound by allowing the resonance of the vibrating air inside the violin “escape”. If too small, then that portion of the sound is reduced to the detrement of sound. Whether varying the size and shape influences dark vs bright sound, I’m not sure and would be interested to know as well.
Another possible variable in the construction of violins is the height of the ribs. A Guarneri copy I have — Cannone model — has high ribs (about 32.5 – 33 mm – vs. roughly 29 – 30 for a Strad model). The Guarneri copy has a darker sound than my Strad version and might be a result of the rib height (or not…).