^you got a point, but I don't know about that comparison. Guitar color has got nothing to do with how it sounds, tuning has everything to do with its:
1) register (if just tuned down like with D standard)
and
2) the kind of chords/harmonization you can practically play (if using more 'alternative' tunings)
Both factors do play a role in what we call "heaviness/darkness".
Interesting example:
He uses that tuning in most of his Cosmosquad material. Notice the unique 'sound' he came up with thanks to it. Kinda "broad" and "dark", not just because the 6th string is tuned down but also because of the kind of harmonization it allows you to emphasize.
What I'm personally against is people tuning down their guitars a shitload just so they sound more metal and badass. They play the same stuff, just in much lower pitches. Not so musical.