Elizabeth II 1965 Six Pence United Kingdom. Error, Variation Or Change Of Color

Greetings everyone.
Elizabeth II 1965 six pence Reino Unido
I'm not sure if this is a mistake, a variation, or if it will change color over time.
I'm asking because I have doubts; I think they were only printed in one color.
I would appreciate your valuable opinion.
Thank you very much.

Utterly faded. probably bleached.

They were printed in two colours. There was an intentional change in the colour from what Stanley Gibbons calls reddish purple to deep claret, in 1958.

The right-hand example has faded to the point where the lighter areas have disappeared. If this was a colour error, i.e. printed in blue, those areas wouldn't be absent.

Imo an environmental or induced chemical changeling and not an error.

The righthand stamp has a cancellation from 1957.

Thank you very much for the information.

The 1957 cancellation promotes the Ninth World Scout Jamboree at Sutton Park, Sutton Coldfield.

I'm not familiar with these stamps but... I have done a lot of experimenting with some of the Canadian stamps printed in colour. Red is the easiest colour to fade. I would put stamps in a window with direct sun and sometimes within a month all traces of red were gone leaving other underlying shades used in making a particular colour. You can Google "lightfastness in printing" and you will learn more than I can ever explain. It is possible that this stamp was exposed to light for a long time or was "treated" with some kind of chemical about which I know nothing about. It's all interesting.

Better still,visit StampSmarter: https://stampsmarter.org/learning/A...gelings.html

The white back - it is difficult, though not impossible, to expose two sides to sunlight simultaneously - and what appears a faded part of one of the two cancellations, as well as the colour, suggest someone used chemicals.

Thank you.