Clamp-tipped Emerald - Cordulie ténébreuse
(Somatochlora tenebrosa)

This collage shows 2 males of different maturities (caught at same a few minutes apart).   As is typical with emeralds, they have brown eyes when they emerge but in most species, the eyes eventually turn bright green.   Also, in the striped emeralds (Somatochloras), many species have stripes and/or spots on the side of the thorax (as this one does) which are brighter when they emerge.   Depending on the species, these stripes or spots will either fade or darken as they mature (sometimes becoming almost brown in colour and blending in well with the brown tones of the thorax making them difficult to notice)