Aggie,
I think there are two parts of a color decision, objective and subjective.
On the objective rational front, there's how the space will be used, and then the subjective, what colors do I like.
That said, I favored a darker base (black) with a heavy application of white and grey flakes to then lighten the base floor color. You're evaluating "charcoal." Objectively, a darker base requires more lighting, as the floor reflects less of the ambiant lumans. It has also been reported that dark floors make finding lost black screws difficult. Conversly and subjectively, the darker base is more dramatic, and I find it stays looking clean even when it's not. I don't fabricate nor weld in my space, so I can opt for a more asthetic choice.
I like your charcoal option myself...
Here's my floor:
Cheers,
E46M3