I took a risk ordering these without seeing them in person first, and I was pleasantly surprised!  The charcoal color is a very nice dark grey (almost black) with a very nice color texture.  The pants are silky smooth and appear well made.  They are super comfortable.  I am going to order another pair.. I just with Amazon had descriptions of what those different color names really mean - for example what color is caviar and twilight?  On my screen they all look the same.  Well at least I can say that the charcoal is very nice.

Update: to answer my own question, I bought two more in caviar and twilight.  The caviar color is essentially black (not flat black, a little bit more shiny or pearly) and the twilight color is a blue-ish black in which the blue tint is barely noticeable.  All the colors are nice and neutral and go well with most shirts.