There has been lots of research into tetrachromacy including the 2010 Journal of Vision Study, known only as cda29. This study identified a tetrachromat using colour testing. The study also stated that up to 12% of women have four cone types.
Nevertheless, research has also suggested that of this 12%, very few can perceive more colours.
In 2014 the Australian artist Concetta Antico openly identified herself as a tetrachromat. In an article published by the BBC, she shared her experiences of tetrachromacy. She told the BBC of how a grey pebble, for example, jumps out to her with many different colours, saying "I'm kind of shocked when I realise what other people aren't seeing."
While research on the condition points to its rarity, subjects like Concetta suggests that it exists nonetheless.