... Out of 180 countries ONLY the United States issues currency that is ALL the same SIZE and COLOR.

Other countries vary the size and/or color to distinguish denomination for the sight impaired.

Also… since 2001 the number of $2 bills being ordered by banks has doubled (122 Million). No one is sure why this trend has occurred, one speculation is inflation. Most commercial establishments abhor the $2 bill since there is no slot for it in the cash register. Club owners have reported an increase in tips when the $2 bills are used in change.