Apple has confirmed the Magic Keyboard, Magic Mouse 2, and Magic Trackpad 2 in Space Gray are "available only at the time of your iMac Pro purchase."
The fine print on Apple's iMac Pro order page spells bad news for customers who were hoping to be able to purchase the Space Gray accessories separately for use with other Macs and Apple devices.
Apple sells the Magic Keyboard, Magic Keyboard with Numeric Trackpad, Magic Mouse 2, and Magic Trackpad 2 in a traditional white color on its online store alongside a few other keyboard and mouse accessories for Macs.
It appears that the black Lightning to USB-A cable included in the box is also exclusive to the iMac Pro at this time, with no option to purchase it separately from Apple's online store like traditional white versions.
Apple could easily choose to release the Space Gray accessories separately in the future, but for now, you may have to resort to eBay or Craigslist if you want a stealthier looking Magic Keyboard, Magic Mouse, or Magic Trackpad.
As far as a black Lightning cable, Apple sells a Belkin one for $29.95 on its website and there are others on Amazon for much cheaper.
Apple released the iMac Pro earlier today, with 8-core to 18-core models available for between $4,999 and $13,199 in the United States. 8-core and 10-core models ship in late December, and 14-core and 18-core models ship by February.
