Off Color / Printed Butterfly Block ?

Hello Everyone,
I received a mix of 'stuff' and come across this lovely block of four, the butterflies, 1977, but as you can see by the colors on the stamps, they are a different color from what I have seen in the past.

Can anyone tell me what has happened? Here is the link to MysticStamp, to show you the colors of the stamps and then below are some photos of the block I have in my possession:
http://www.mysticstamp.com/viewProd...?sku=1712-15

You can see in the second photo, that there is a glossy / matte over part of the stamps as well.

Also, I am trading all my MNH / used USA stamps including this block. If anyone is interested, who has traded here before with good standings, I would be most happy to take offers. I collect foreign, I love overprints, old, bi-color, mono, anything with interesting scenes, ships, trains, BOB, I am not too picky but prefer MINT, don't care if backside has hinge / marks, flaws, just like a nice (mostly) clean frontside.

Thank you,
Sue
My SCF ID: SueStamps
Here are photos of the block:

Hard to say, but I suspect that the stamps have been exposed to strong sunlight or a chemical which caused the change.

I would guess that these are errors. It's possible the colour has leached out, but when you look at the originals, you see for example, purple spots on the lower wing of the butterfly top-left, and orange wing tips on the butterfly bottom-right. I don't see any shading on your ones to suggest it has been transformed to grey - it seems like the colours are simply missing. My guess is that this was the first layer print, just black/grey and that the other colours were never applied.

That matte finish you speak of is probably the taggant. I think these was just exposed to sunlight for a very long time as traces of the colors are there but not vibrant. Hope that helps some? -Jeff

I concur with ILS and jarnick, an environmental color changling and not an error/freak.
Don

That's a lot of color to fade out. under magnification is there any color?

You should contact Mystic Stamps and others about these stamps to see if they may be a missing color variety.

Thank you all for the replies. Great idea about contacting MysticStamp! I will do so. Here are some close up photos especially close up of the 'matte' like finish, so puzzling! See below:

Can't say anything about the color change, but the shiny blocks over the face of the stamps is definitely the taggant. Shine a UV light on them (if you have one); they should fluoresce a bright yellow green.

Robert

I received a reply from MysticStamps regarding this off color butterfly block below. I still have it if anyone is interested. Thank you, see below:

Dear Sue,

Thank you for your email. Your stamps (Scott #1712-15) look to be a type of Error, Freak, or Oddity (EFO). Unfortunately, Mystic does not have any references stating that one exists for this set. You may want to contact the Philatelic Foundation at 1-212-221-6555 and the Scott's Publication with your find. The Scott's Publication's email address is http://www.scottonline.com/contactus.

Please let us know the result of your find. It is very exciting to come across a possible new find. Good luck and happy collecting.

Sincerely,
Mystic Stamp Company
Processing Department