It looks like users will soon have the option to assign different skin tones to certain emoji through a "skin tone modifer" panel — when clicking on a particular emoji, you can then choose from a variety of different tones rather than just the default option. Judging from the Mac Rumors screenshots, this feature hasn't been fully implemented yet, as there are still blank spaces and placeholders for various new emoji as well as the specific skin tones, but this should be fully realized by the time 10.10.3 is released.

Apple has also expanded the categories that emoji are grouped into, a much-needed change — the huge variety of emoji currently found under the "bell" category is simply ridiculous at this point, for example. Users will also be able to scroll through a complete list of all installed emoji rather than paging through lists, though the option to skip around the various categories will still exist.

There's no specific timeframe for when OS X 10.10.3 will launch, but Apple said the Photos app would be available this Spring — and since we know it'll be included as part of that OS update, we should see these new emoji features roll out around the same time. Of course, it's worth remembering that this is just a developer seed, so things could be changed and removed between now and then.