If you happen to see days of the week, months of the year, even individual numbers and letters in colour, you are a synaesthete. "What colour is Thursday?" might seem like a strange question to some, but If you have synaesthesia, you may just have an answer.

Synaesthesia is a psychological and neurological condition that results in the merging of senses that aren't normally connected. For those who have never known a green Thursday or a yellow November, it’s difficult to comprehend how this unusual condition works. Most people have five senses: sight, touch, hearing, taste, smell. For synaesthetes, there is an overlapping of two or more senses. For example, someone with synaesthesia may hear colour or see sound.

There are two different types of synaesthesia: projective and associative.

• Projective synaesthesia – seeing actual colours, forms, or shapes after sensory or cognitive stimulation.
• Associative synaesthesia – feeling a strong, involuntary connection between sensory and cognitive stimulation and colours, forms, or shapes.
  

Some types of synaesthesia are more common than others. Grapheme-colour synaesthesia may be the most well-known, but there are many types of synaesthesia:

• Grapheme-colour synaesthesia – associating letters, numbers, days of the week, months of the year and so forth with a colour.
• Sound-to-colour synaesthesia – associating sounds with colours, usually coloured shapes.
• Number-form synaesthesia – visualising a number map image when thinking of a number.
• Ordinal-linguistic personification – associating numbers, letters, months, and so forth with certain personality traits.
• Lexical-gustatory synaesthesia – associating a word or phoneme with a certain taste.
• Auditory-tactile synaesthesia – sounds elicit tactile sensations in various parts of the body.
• Mirror-touch synaesthesia – when someone else touches something, you feel what they would feel.
  

Synaesthesia is not a reaction that happens selectively or can be “switched off”. In the types of synaesthesia involving projected colours, those colours do not interfere with colours in the surrounding environment. Rather, both are perceived as separate and distinct. For example, someone who perceives individual numbers as colours still sees the numbers in whatever colour they are written, but they also experience either a very strong association between the number and a particular colour or very clearly see that colour projected in some way, maybe glowing around the figure.

Is synaesthesia something that colours your world? If so, maybe you have an answer the question, ‘What colour is Thursday?’

Sources:

1. BBC.
2. The Psychologist.
3. Spectator.
4. Mental Floss.
5. Better Help.