The most common form of synesthesia where individual letters of the alphabet and numbers, are "shaded" or "tinged" with a color. The color of the letters varies from person to person but there are some commonalities (A is usually red) 



Like all forms of synesthesia, grapheme is involuntary and last a life time. Also, because of the extensive knowledge of the visual system, it is the most studied form of synesthesia.

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Frequent letters seem to be paired with frequent colors and the coloring of some letters is based on the first letter of the word. For instance 'b' being blue.  

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It is hypothesized that the colored letters are a result of activation in the 



1. Fusiform Gyrus: Involved in color, letter and word processing
2. Visual Cortex: Imaging and visual creation