I guess I'll go against the grain and opine redundancy only because it's the same hardware. I definitely understand the interest in both of these colors though. I would get black with ghw to change it up.
I have a noir b30 and got a graphite b35 last year....i ended up rehoming the graphite as i felt i didnt need both (though graphite is stunning) and preferred the b30 size.
35B clemence PHW.
Graphite. The colour appears to vary depending on what you put with it (the colour of your outfit).
Plus, everybody has black. Graphite is a bit different.
I think they are redundant and would pick the black. Was never a fan of black bags until I got my black clemence Kelly PHW. It's just so easy to wear and classic.