I've not seen it that obvious before. In the third over printing, the black seal, directly above the left side serial #, is printed and I suppose it could have darkened the serial number, but I'm not that versed on the process of inking. I'm sure SteveInTampa or one of the other currency experts would know.
I don't believe it is 2 different colored inks. Yes the lower left is a little darker than the upper right. Depends on the way the plate/ bed was inked and which side got more and which side got less.
The green ink can be attacked by chemicals in the environment causing it to fade, change shades or even look yellowish. In addition, all the green on the front is printed at the same time, so there really isn't a way for there to be 2 diff inks. Your note has seen a lot of circulation and was exposed to something that caused part of it too fade
It's more dramatic than I've seen before, but it'll probably be not-too-uncommon going forward. The new computerized numbering heads that are used on LEPE are so large that they can't be packed tightly enough together to print all the serials on a sheet in a single operation. So there's one set of numbering heads that print the left serials on all the notes on the sheet, and another set that print the right serials on all the notes on the sheet. And if the ink feeding one batch or the other isn't mixed just right, you get a note like this one. (The older COPE lines print all the serials on a sheet in one pass, so they presumably can't produce an effect like this. But COPE does print the green seal separately from the green serials, and occasionally they do appear to be two slightly different shades of green.)
Highly unusual. I thought at first that lighting may be influencing the colors so I tried to duplicate the photo with a note of my own. It does make a little difference, but not as much as the OP’s note.
