The iOS 8 and OS X Yosemite beta 2 updates are part of Apple's ongoing efforts to address diversity, and it's extending beyond organization and into software, with a much wider array of cultures and ethnicities for face and hand symbols.
Emoji have become popular because they're efficient, sometimes amusing, but mostly humanizing. They allow for the inclusion of emotion and feeling beyond what plain text can transmit. It's for that very reason that emoji need to be inclusive — so that people everywhere can see themselves reflected in their use.
The way it works is like this: The iOS 8.3 or Yosemite keyboards starts off with a "neutral" (i.e. classic yellow) emoji. Tap/click and hold and you get five alternate skin tone options. These are based on the Fitzpatrick scale for standard dermatological representation, as adopted by the Unicode Consortium.
In addition to the flags and skin tones, there's also greater gender diversity for families, new electronics, and more. No word yet on some of the more controversial elements of the new Unicode standard.
iOS 8.3 and OS X 10.10.3 are still in beta, so it's possible that the exact number, style, color, and character of the new emoji will change between this beta and its release — expected some time this spring.
It's great to see Apple using its popularity and power to push for more and better inclusivity. Hopefully it's just the beginning, and for all platforms.
3:30pm: Updated with implementation details and OS X 10.10.3 integration.