I am sure not many persons will be seriously interested in this, but I just feel the urge to share some information about this.
In 1948, Yugoslavia issued a set of 3 stamps to commemorate the Zagreb Fair (SC#236-238)

Now, with this set there is a legitimate error, on the 1.50 dinara (SC#236) which a number of sheets (I have no clue how many) were NOT put through the blue stage, and thus there is no blue in the portion of the flag that should be blue.
Recently, I have noticed that there are several of the 5.00 dinara (SC#238) listed on various sites as being an error "missing blue," and offered at prices comparable to the real error 1.50 dinara (SC#236)
If anyone finds these listings and thinks they are actually "missing blue" errors, I would like to present a case to the contrary.
The following image was captured from an actual auction listing. I do not care to identify the seller, as my purpose is not to bash the seller, but rather to inform possible buyers.

As you can see by the red arrow, there is a lot of white space in the area that should be blue.

In this image, using my primitive photo editing skills, I have highlighted in black the areas that should be blue.

And in this final image, I have shifted the layer to show the highlighted areas from above image.
As is clearly visible, the blue is there, just shifted (mis-aligned).
I suppose this mis-alignment could be considered as an "error", but I think it is more of just a poor quality product.