Going on our hols on Saturday, so got our US$ today. I remember they used to be all green, so you really had to look at them to see what denomination you had as all the notes are the same size, but now they have different colour tinges to them. When did that happen?, as they were still all green in June 2005.
There have been recent changes to the $10 and the $20 dollar bills, certainly since June 2005. But as you say it is only the tinge. Also when notes are new it is more obvious, once they've been a few different pockets and probably rolled up for drug use etc. it is not so noticable.