I have the 14mm version of this ring and needed to have it sized up. You can order directly from DY but it takes several weeks! I was too impatient to wait that long so I let Neiman Marcus send it to one of their preferred jewelers. On the underside of my finger, you can see a line and a smooth finish. But, who looks on the underside of the finger? Nothing about the sides, top, or beauty of the ring has been taken away!
As for the color - it depends. I was absolutely in love with the Onyx for years! Finally, when I went to the store to purchase it, I ended up leaving with a Smoky Quartz! It's still got the darkness that I love, but isn't opaque like the Onyx. Shop around, until you find the one you love!!!