$20 Reverse Is Really Dark - Printing Error?

See image below. The reverse side of this 2009 $20 is really dark but I do not know if this is something that happened after the bill was in circulation or if it is a printing error. The scan does not do it justice. It is really dark, almost a dark blue-green color covering the entire reverse. There is also some darkening on the obverse at the outer edges. Also note that the security strip on the left side of the obverse can be clearly seen as a white stripe. This is not due to the scanner bulb shining through. It looks that way normally. The ink coloring of the blue eagle is really faded where that stripe is located which is normally not the case on other $20 bills I have looked at. Are these printing errors and if so, does it have any value?