And here I thought all the American money seemed monochromatic.

You’re thinking of older US paper currency, which was shades of green for a lot of its history. Over the years they’ve modified it to include other colors and introduced numerous security features, all in an effort to make it very difficult to counterfeit.

Here are a couple of examples of how bills looked when I was young:

numismaclub.com/…/10_1981_cu_trio_chicago_il_frn_…

usrarecurrency.com/…/1996$50FRNSnAA20022001A.jpg

Mate, your money does still seem monochromatic to modern eyes. I use it when I visit, and the other notes don’t have that rainbow on them. I admit I am rarely exchanging more than fifty US at a time . I’m comparing those that I use to modern notes.

And security features? The shops there still accept cheques. I was surprised the economy still functioned when I found that out.