I have noticed a number of Parker 51s being advertised, on eBay recently as 'Green'. Most of them are, in fact, the much more common 'Teal' colour. Given the poor colour rendering of the actual colour it is sometimes difficult to tell, on the screen, which is which. I usually resort to photographing dark coloured pens against a coloured background to prevent them all appearing as black.
This is a Forest Green pen:
And this is a Teal pen:
It is easy to distinguish between the two colours when shown together but if a seller just shows the Teal and describes it as green there is room for confusion.
Just to confuse matters more the Parker 61 was made in Teal, except it wasn't. the colour of the 61 corresponding to Teal is, in fact, Caribbean Blue:
I photographed this pen against a garish background as it showed the colour more accurately than a plain one.