Cayman Island color ?

This is a back of the stamp photo and i think is prove that is not Sunlight damage since the stamp is in MNH condition.

ibb.co/d5h2TMh

I only have 6 Cayman Island stamps so I'm certainly not expert. The upper stamp in this composite image, pulled from the internet, is intended to show the stamp with what I assume is normal coloration. I wonder if your stamp (at bottom for comparison) is a changeling caused by sulfurization/oxidation. In 2009, Scott provided a value of $200 for a "gold omitted" stamp -- I have no idea what today's value is. If it is still close to $200, it would cost you about 25% of CV to have it expertized. I checked the both the Philatelic Foundation and APEX databases and neither has issued a cert on this stamp.

Thanks for this interesting thread, Dimitris (dleogr ).... you are posing an interesting question!

I had wondered if your stamp could simply be a changeling, but I had not really been thinking that it could be sulphuretted, because I normally associate that problem with stamps from the classic era.  Thanks to Steve (tomiseksj ) for suggesting it in this case, which had not really occurred to me.

As I look at it now from a fresh perspective, I think Steve is probably right.  Sulphuretting is a not-so-common term for what happens to colors on stamps that have been exposed to air with sufficient sulphur content.  Many collectors erroneously refer to this as oxidation, which ironically, is actually the remedy for a stamp which exhibits sulphuretting!

The most susceptible colors to change due to sulphuretting that I have seen are orange, which goes to brown or sepia; red, which goes to lake or brown; and royal or bright blue, which goes to navy or even blackish.  In your 1/4d stamp, it appears to me that the image of the painting, could in fact, be sulphuretted from its original red shades to a brown ones.  Unfortunately, it is much more likely to be a color changeling than an undiscovered color-omission printing, but who knows?

The only way I know to test if it is a color changeling from sulphur is to soak the stamp in a hydrogen peroxide solution, which will re-oxidize the surface and bring back the original color.  But that will only work if the stamp has been sulphuretted.  If it is a true printing error or the color has changed for another reason, the peroxide treatment should have little or no effect, other than to remove all the gum from your unused stamp!

If you really want to find out if you have an unlisted rarity there, I think Steve is right to suggest getting it expertized.

Hope this helps a little.  It's a tough question you have asked! 

For Commonwealth stamps the best experts would probably be the Royal Philatelic society of London, but to a Non member the fee is likely to be around Euro 35.plus mailing costs by registered mail , putting you about €50 out of pocket for what is probably going to be a huge disappointment.

It is extremely unlikely that there would be a only a single stamp in a sheet of 100 with missing red ink in the printing. So after 70 years where are the others from the sheet?
There are none reported to the catalogue.

I still feel the most likely explanation is a changeling due to sunlight . If it had been in a display card in a dealer’s window for even a few weeks the red would fade even if it is mint neverhinged on the back.

Expertising is expensive and You must be prepared to be given bad news. Are you near a city where there is a stamp dealer ? It would be sensible to ask his opinion before paying for a certificate.