Thankyou all for the kind words. I will admit to a certain perverse satisfaction to showing off new finds here on SCF.
As to the colour of the stamp, I have never had much skill in differentiating the various shades of this issue.
Here I've scanned it with my two known #65s. There's a slight variation, but I wouldn't know how to classify it.

I made a point of scanning them all on the same background (the envelope) to reduce any tonal influence. And of course, scanners, monitors etc must be taken into account. But I think this is a fair comparison.
Lower right corner. Possibly a #64?