This is a type specimen showing color fonts. You only see black type above? You might consider firing up Firefox (version 26+) for the full glory. The text above is set in OpenType fonts with embedded svg. Things might change but as of this writing (October 2014) the format is supported by Firefox only.
Click in the text and type away to test it yourself!
Why use color fonts only for emoji? Color is more than a pile of poo and red hearts! You can find some information about the format and how the fonts were built on this site.