20 Dollars Federal Reserve Note, colored

The 2004 series marked the second major redesign of the $20 note and the first to introduce background color to U.S. currency since the demand notes of the Civil War period — a concession the Federal Reserve and Treasury had long resisted, largely on the grounds that Americans expected their currency to be green. Counterfeiting pressure, particularly from high-quality offset printing operations in the Middle East and South America, forced the issue. The color-shifting ink on the numeral shifts from copper to green depending on viewing angle, a feature that proved more effective as a public authentication tool than most of the embedded security elements that preceded it.

The security thread is position-encoded to the denomination — UV light reveals "USA TWENTY" — making it physically distinct from threads used in other denominations, a deliberate anti-substitution measure introduced after bleached lower-denomination notes were used as stock for counterfeit hundreds.