I have both the right ruthenium in small and right black carbon in medium. , for those who want to see comparisons. Both are shiny. The ruthenium is sort of a gun metal color and the black carbon is like a black metal, but also almost deep brownish, if that makes sense (where the shine is).
I have tiny, bony wrists (about 5.5") and they fit fine--I was told I could squeeze them down to fit perfectly (I'm small, but strong... Squeezing them isn't an issue, but opening them while on my wrists is, so I have them just at the point where it's a struggle to get them on and off).
I also feel that the medium is a bit big on my short arms (I'm muscular, so, combined with my tiny wrists , short arms, and strong forearms, my arms are NOT straight and the medium isn't flush from top to bottom), but I LOVE the medium's look. If it would fit, I'd get the large, but that's impossible with my arms.
Here are some pics. I found the silver to be too flashy for me (bc of how big it looks on my arms), but I took a pic next to a white gold ring so you can see color. The last image, where the ruthenium looks silver is much lighter than it is in person, just so you can see detail between the two.