Identical Stamps, But The Colour A Bit Off

Flipping through some stamp albums, I noticed two identical stamps, one of them, the colour seems a bit off. Running out of ink or what?

Could that be a smudge from the paper the stamp was on? To my eyes it looks like there's even some paper remains left in the upper left corner of the stamp.

The stamps are of two different shades mostly in the browns, but quite obvious in the birds. The green must be a stain in my opinion.

Just suspected some remnant of the envelope may have caused the Color changeling, due to the glue used. The chemicals or other substances in the glue may caused some bleaching on some stamp dyes.

Just read this information from the National Library.

A couple of things to take into account:

• the roughly circular shape of the colour change


• the way that all the colours in that circle have been changed, even a little of the blue at about 3:00

My guess is that something (perhaps a household cleaner) dripped onto the stamp causing the colour change. It is still a keeper though in my opinion.

It looks as if something has been spilt on the RH stamp.
Apart from that, when the 70c kookaburra, 90c kangaroo and $1.20 cockatoo definitive stamps were issued in 1993, the word Australia and the denomination across the top of each stamp were printed in orange. In later reprints the wording was issued in a browny-orange colour. In the case of the $1.20 cockatoo this happened from April 1998. The two stamps above appear to be SG1370a (on the left) and SG1370 (on the right).

It looks like some staining from the envelope.
Here's the two stamps where you can see the difference in the shades of the wording.