Answer:
Synesthesia is a condition in which one type of stimulation evokes the sensation of another; as in several senses. You don't really "get" synesthesia, you can inherit it genetically from your parents. It is often times passed on through the x chromosome, which explains why women are several times more likely to have it than men.
You are most likely born with it and it is very rare. People who have lexical synesthesia see color in letters, numbers, or sounds,(and sometimes even in all three or just two). I learned a lot about it from " A Mango-Shaped Space" by Wendy Mass. This book is great, try it!