I like all the colors of iOS devices, but for the iPad Pro, for some reason, the black bezel seems most appropriate. Somehow, black seems most pro to me, it is least distracting when using illustrating apps and the blacks on the screen blend beautifully with the bezel. it became more pronounced on newer iOS devices that have even less gap between the LCD and glass and higher contrasts. iPad Pro with its Photo Alignment has some really deep blacks. I noticed how my SG iPhone 6 also has this effect, as well as the Apple Watch - when a screen has black elements, they blend with the bezels and look awesome. For example, when watching movies, the horizontal black bars merge with the borders, when reading comics, the vertical ones do the same, etc. It just looks great. Pro apps like Procreate and Sketchbook also look awesome - for example, Sketchbook looks the same like on my iMac (white canvas surrounded by a black bezel) and Procreate reminds me of a dark-themed Photoshop on the Mac. I am really happy with my choice.
All iPads are pretty and silver and gold ones are also striking, but for me, the SG iPad Pro simply looks the best. But no matter what color you chose, it's great and looks awesome.