Synesthesia only occurs in some people

In another study, synesthetes created novel color associations
for unfamiliar letters after learning what the letters were.
So because it relies on a connection between ideas and senses,
this mental phenomenon underlying synesthesia
is known as ideasthesia.Synesthesia only occurs in some people,
although it may be more common than previously thought.
But ideasthesia itself is a fundamental part of our lives.
Virtually all of us recognize the color red as warm and blue as cold.