Cheers guys.
So onto more specific questions if I may.
There are various shades listed such as green on greenish paper, yellow green (SG + Scott) + dark green and very dark green in Y+T.
Would you say this is green on greenish as it is much darker than any other images I can find?
Would 10% of cat. be a fair value?
Oh and it has a mark on the back possibly owner or expertisation.

It looks similar to the mark of Dejan Tubinovic but I lean towards owner as most of the early items are marked in this booklet.