Avengers #10
Magenta and Yellow Printing Error

Marvel Comics, November 1964.

There are two variants of Avengers #10, an initial printing error copy (1st image below) and a corrected copy (2nd image below):

There are four colors (magenta, cyan, yellow and black) used in the print process to create all the colors on the cover of these comics (they are mixed at various percentages). In this case the magenta was applied to the yellow plate and visa versa creating the effect in the error copy in the first image above.

CGC have curiously decided to give the error variant a green qualified label (see comic illustrated above), noting the color switch, whereas a later very similar error on Fantastic Four #110 was on a blue label (below) and had a separate entry in the census as a variant:

There are usually a couple of the Avengers #10 error variants for sale on auction sites such as ebay so are not difficult to find but are usually at least double the price of the corrected copies.