The other night I had the opportunity to get a private lesson on my euphonium... (Long story, but had the opportunity to work with a low brass guy)
... Anyway, interestingly enough he said I played it like a trumpet and played it 'Bright' versus the darker sound that I could get from an Euphonium... He mentioned chin down even more, open, slower air larger aperture, etc. Granted I know that if I pull out my flugel horn it is always going to have a really nice 'rich' dark sound to it compared to my trumpet, but wondering how much you change the 'bright-ness' or 'darkness' of your sound just by habit and how you adjust your embouchure or speed of air, etc.?