The US is too full of people who hate change too much to pull off a currency change other than incrementally. Or changes that are completely hidden, like coppertoning those zinc pennies they use now, since copper's so expensive. We've had dollar coins since before we were a country, but once people finally got used to paper money, with the dollar as the smallest denomination, efforts to eliminate it and replace it with a coin have consistantly failed. For a new country, we desperately cling to our "traditions"!
Change like this has to be done top-down, and our psuedo-republic/democracy (it's really neither) can't get away with it (hell, it can't even reform health insurance decently...). As a limited-sight person, I know it would be better to have distinguishable bills rather than having to sort them under a bright light. I know some people who go to great lengths to keep it all sorted out, and most have to depend on the honesty of the clerk.
But change like that ain't gonna happen anytime soon!
Oh, and the "now I'm re-dying it!" comment... so she's got the dye on while she puts up the laundry? Sounds hazardous, unless all the clothes are black, or you don't mind purple spots...