Colors in Carey's world have properties that most of us would never dream of: red is solid, powerful and consistent, while yellow is pliable, brilliant and intense. Chocolate is rich purple and makes Carey's breath smell dark blue.
http://www.livescience.com/169-rare-real-people-feel-taste-hear-color.html
Another common form of synesthesia is the association of sounds with colors. For some, everyday sounds such as doors opening, cars honking, or people talking can trigger seeing colors. For others, colors are triggered when musical notes and/or keys are being played.
https://en.wikipedia.org/wiki/Synesthesia
Caroline. I've had synesthesia all my life, and in the research of synesthesia you HAVE to be careful with the wording. The best way is to get some actual input from synesthetes. For example, certain numbers remind them of particular colors is quite misleading: we SEE the actual letter or number in color.
http://thechart.blogs.cnn.com/2010/11/17/on-the-brain-when-numbers-have-color-synesthesia/
Time related words-colour synesthesia is the second most common with a prevalence rate of 22%-62%. Music-color is also prevalent at 18%, some studies found that music-color was shown in 41% of patients. Some of the rarest are reported to be auditory-tactile, mirror-touch, and lexical-gustatory.
https://en.wikipedia.org/wiki/Synesthesia
I associate colors, smells and tastes with words, individual letters, numbers, groups of numbers and ordinary objects. Some objects have both smell and color associations. Most, in fact. Some of it, though, has to do with conditioning.
http://thechart.blogs.cnn.com/2010/11/17/on-the-brain-when-numbers-have-color-synesthesia/
She can also taste them, and hear them, and smell them. The 20-year-old junior at the University of Maine has synesthesia, a rare neurological condition in which two or more of the senses entwine. Numbers and letters, sensations and emotions, days and months are all associated with colors for Carey. The letter N is sienna brown; J is light green; the number 8 is orange; and July is bluish-green. The pain from a shin split throbs in hues of orange and yellow, purple and red, Carey told LiveScience.
http://www.livescience.com/169-rare-real-people-feel-taste-hear-color.html
The colors of letters and numbers in this photo illustration of Ingrid Carey, by Ingrid Carey, match up with what she sees. Credit: View full size image. View full size image. When Ingrid Carey says she feels colors, she does not mean she sees red, or feels blue, or is green with envy.
http://www.livescience.com/169-rare-real-people-feel-taste-hear-color.html
Synesthesia (also spelled synaesthesia synæsthesia or; synaesthesia from The Ancient greek σύν, syn, together and αἴσθησις,  aisthēsis ) sensation is a neurological phenomenon in which stimulation of one sensory or cognitive pathway leads to, automatic involuntary experiences in a second sensory or cognitive. pathway
https://en.wikipedia.org/wiki/Synesthesia
This study also found that people with synesthesia generally have more white matter, indicating increased connectivity, in the fusiform gyrus, a brain area involved in the processing color, numbers, letters and faces.
http://thechart.blogs.cnn.com/2010/11/17/on-the-brain-when-numbers-have-color-synesthesia/
For example, perceiving letters and numbers (collectively called graphemes) as colored would be indicated as grapheme → color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated as tone → (color, movement) synesthesia.
https://en.wikipedia.org/wiki/Synesthesia
what's it called when you hear colors
It called Synesthesia when you hear colors. Hearing colors are called synesthesia.