Synesthesia

Synesthesia is actually the coolest thing ever. Seriously. 
Synesthesia is a condition in which one sense (for example, hearing) is simultaneously perceived as if by one or more additional senses such as sight. Another form of synesthesia joins objects such as letters, shapes, numbers or people's names with a sensory perception such as smell, color or flavor. Synesthesia occurs when stimulation of one sensory pathway leads to automatic, involuntary experiences in a second sensory pathway. 

Synesthesia can involve any of the senses. The most common form is colored letters and numbers. This occurs when someone always sees a certain color in response to a certain letter or number. For example, a person with synesthesia might see the word "hello" as yellow or the number "4" as dark blue. Some people with synesthesia hear sounds in response to smells, smell in response to touch, or  feel something in response to seeing something. Almost combination of the senses is possible. There are some people who possess synesthesia involving three or even more senses, which is very rare but insanely cool. 

Different people with synesthesia perceive things differently. For example, one person may see the word "lamp" in green, while another sees "lamp" in a dark purple. One person may feel upset at the sight of someone mowing the lawn, while another person may feel content and at ease. Also, women and left-handed people are more likely to have synesthesia (whether they realize it or not). 

Note: People with anesthesia may actually be able to taste the rainbow.