Why aren't "Green cards" green?

The U.S. Immigration and Naturalization Service (INS) gave us this answer-"What know as the 'green card' used to come in a variety of different colors at different times in our history. Still referred to as 'green cards' for the same reason dismissal notices are called 'pink slips,' etc.. In each case an idea was originally associated with an actual item of respective color."
A lawful permanent resident (LPR) alien living in the United States may carry a card that is not green, but refers to it as a 'green card.'
The alien does so because those benefits came into being at the time when the card was actually green. The green card is formally known as the Alien Registration Receipt Card, form I-151 or I-151. The first receipt cards were form AR-3 and were printed on white paper.
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