Currency is regularly redesigned about every 7 years anyway. Sounds like a couple of those changes could be easily adopted (although, I hate the idea of the bills being different sizes, I think that one will never happen.)
Also, most currency is already color coded. It is amazing the number of newspaper articles I have seen about this that claim that all American currency is the same color.
Huh? All American currency is the same from denomination to denomination within each series. Where does the color variation come in?