Help Two Pence Great Britain 1858

2d blue plate 15 with Large Crown watermark.
What really caught my attention is the colour. It is not the normal blue usually seen online. In reality it is a very deep intense blue with a slight greenish/petrol tone.
The ink seems heavily saturated and penetrates deeply through the paper, even the back and the watermark area appear strongly blue.
The photos do not fully capture the depth and tone of the colour in hand.
Have searched many examples online and cannot find another with quite the same appearance.
Could this be a recognised shade or just an unusual but normal variation?
Thank you

The top right appears like someone has been rubbing something off. The left side, also, looks suspicious. Around the eye is more ecidence of a blue cancel that either has seen an attempt at removal or has run (hot water soaking?).

Thank you for your opinion. The photos unfortunately appear much lighter than the stamp does in hand. In reality the colour is much darker, denser and more intense.
I understand your point about possible soaking or alteration, although in hand I do not clearly see obvious rubbing or cleaning. The unusual appearance is exactly why I posted it, as I have not been able to find another example with quite the same colour and ink saturation.
I appreciate the feedback and would be very interested to hear if anyone has seen similar examples before

It is not so much the colour itself as it is the rubbed spot in the NE corner and the ring around the eyes.

This photo reflects the real colour much more accurately.

Do you still think in this new photo the same?
Thank you

Looks like the paper may have been stained by potassium ferrocyanide, as in the Penny Reds on blued paper. If that is the case, you'd have a Prussian blue pigment on top of a cyanotype.

That is very interesting, thank you. Do you think this appearance could be the result of an original ink/paper chemical interaction or ageing process, or would you consider it more likely to be the result of a later chemical treatment or manipulation?

Sorry, no idea!

The new image shows circles with crosses in blue ballpoint ink in the NE corner. This stamp has been altered.

Thank you very much