Different skin tones and hair colours of emoji characters are helping boost diversity, and are rarely abused, a study of Twitter posts has shown.

Fears that a range of skin colour options for the social media icons might be used inappropriately - in provoking antagonistic racial sentiment - have been unfounded since their introduction in 2015, according to the study by researchers from the University of Edinburgh in the UK.

Drawing on a sample of a billion tweets, researchers found that most people who chose to modify their emojis opted for a skin tone that aligned with their own.

In tweets where the selected skin tone was different from that of the user, posts were found to be mostly positive.

Users with darker skin, according to their Twitter profiles, were most likely to modify their emoji, while users with light skin were less likely to make any changes.

This underlines the importance to users of being able to express their identity online, researchers said.

"The introduction of skin tone choices for emojis has been a success in representing diversity and their extensive use shows that they meet a real demand from users," said Walid Magdy, from the University of Edinburgh.

Almost half of modified emojis used a light skin tone because most users are white, the study found. The darkest skin tones were used least throughout most regions of the world, even in Africa, perhaps reflecting the lack of internet access in developing regions.

"This result should encourage the addition of more emoji options for self-representation adding to those that have been recently made available, such as red hair," said Alexander Robertson, from the University of Edinburgh.