Hi, Just found these two while sorting some stock.  Thought I'd share with you. Rather nice.   Motto: always study carefully and  preferably in good light, and hopefully with a known shade for comparison.

The one on the left is SG 255a mint hinged, and the one on the right is SG 255, also Mint with  extremely very light hinge.  The right one has a 2013 catalogue value of 1.50GBP, while the right one is catalogued at just 16.0GBP. Deep olive green shade versus olive green.  I hope the scan shows the difference clearly.   Both will be listed together in my Bidstart store over the next few days. A chance to fill a gap in your collection maybe.

Best wishes... Michael   www.cddstamps.com