Grapheme-color synesthesia is described as a synesthete perceives a color when they see a number or a letter. This is the most common type of synesthesia with 64.4% of all synesthetes experiencing it.

To test this, Baron-Cohen created the synesthesia battery test (aka "The Battery") where a person would choose a specific color from 16.7 million options and the amount of times that color is chosen consistently determines the genuineness of the synesthesia. A score less than one indicates a person with synesthesia.

These synesthetes have been found to have an enhanced working memory and episodic memory through Rothen, Ward, and Seth's study in 2018. Additionally, these synesthetes have been shown to discriminate between colors very well.