Emoji, the pictographs that are liberally sprinkled throughout iMessages, texts, and tweets, have long been criticized for lacking diversity. Of the 59 food emoji available on most software programs, there exists neither a taco nor a sandwich. Worse, the human emoji (the runner, the swimmer, the waving and clapping hand gestures) are mostly depicted with light skin tones. Emoji lovers have long advocated for an update to better reflect a range of different skin colors and ethnicities.
In March, partly in response to the Miley Cyrus tweet above, Apple pledged to make iOS emoji more ethnically diverse by working with the Unicode Consortium, a non-profit that develops, maintains, and promotes international software standards, including emoji. It released 250 new emoji in June, but many still believe there are too few emoji representing people of color.
The UC’s plan for its next emoji update may better address the problem. According to this working draft:
People all over the world want to have emoji that reflect more human diversity, especially for skin tone. The Unicode emoji characters for people and body parts are meant to be generic, yet following the precedents set by the original Japanese carrier images, they are often shown with a light skin tone instead of a more generic (inhuman) appearance, such as a yellow/orange color or a silhouette.
Unicode Version 8.0 is adding 5 symbol modifier characters that provide for a range of skin tones for human emoji.

Each emoji that represents a person or face would have a default color that’s intentionally non-realistic, such as a strong yellow (though perhaps purple would be preferable), and could be modified to match one of five skin tones.

Ideally, this would be as simple as having a color palette pop up when a user presses on the default yellow (or other non-realistic-colored) character.
The Unicode Consortium did write this disclaimer into the draft for the coming update:
Of course, there are many other types of diversity in human appearance besides different skin tones: different hair styles and color, use of eyeglasses, various kinds of facial hair, different body shapes, different headwear, and so on […] It is beyond the scope of Unicode to provide an encoding-based mechanism for representing every aspect of human appearance diversity that emoji users might want to indicate.