Paper money has been used in the United States since the American Civil War. Unfortunately, during that time nobody took very good notes on why some of the choices about how money looks were made.
Green is a very common color for money. While we are unsure why it was picked originally, we do know why it was kept. Dollar bills used to be much larger, but in 1929 bills were made smaller, the size they are now. At that time, someone did take good notes!
The green ink was kept because it was easily available in large amounts, so lots of money could be printed. The ink itself was strong. It doesn’t rub off easily, which makes it a good choice because people are always touching it!
The ink that makes green ink is actually made of several different color inks. The special combination is kept secret, so that people can’t counterfeit the bills. Counterfeiting means making fake money, which is a serious crime. It’s not fair for some people to have to work for their money, if others just make fake copies.
The biggest reason dollar bills are still green is tradition. Money has been green for so long, it’s hard to imagine major changes to it. The nickname for the U.S. dollar is actually “greenback” because of the green ink used to print them.