Technicolor Money

On a recent trip to the UK I had to get used to British currency. The coins were a problem but not the banknotes since each denomination was a different color. The £10 note was not only a pretty color but it had a picture of a famous scientist.It's hard to imagine an American bill with a picture of Darwin. It's also hard to imagine an American bill that's any color but green. Why is that? Is America the only country that does not have technicolor money?

I asked my American travelling companion about this but he didn't seem to care. In fact, I got the distinct impression that he preferred boring monchrome money.