Length 4 mm. A well-marked species with 3 large spots on the pronotum and usually black streaks along the forewing, over a greenish background - these can sometimes be faint.  The nymph is also distinctive, with yellow and black banding, 

Good quality photographs taken in the field or from a specimen

mainly on Alder

Adult: July - October

Common (ref: UK Auchenorrhyncha checklist 2021)

Occasional

https://www.britishbugs.org.uk/homoptera/Cicadellidae/Eupterycyba_jucunda.html