Space and arrow keys to continue So you may be wondering 'what on earth is synesthesia?' Synesthesia is something that everyone has to a degree. It causes you to asign things like days and letters and numbers colors. For example, my Tuesday is a lighter green. It also makes you remember certain things if you smell a certain smell or see something particular (deja vu). It is really cool and I want to share my synesthesia with you guys.