Adult Balkan Green Lizards (Lacerta trilineata) and Western Green Lizards (Lacerta bilineata; western Europe) and Eastern Green Lizards (Lacerta viridis; eastern Europe) are very difficult to distinguish in places where their ranges overlap.
Usually, adult Balkan Green Lizards have yellow throat markings and adult Western and Eastern Green Lizards have blue throat markings.
Lacerta viridis is absent on Lesvos.
Immature Balkan Green Lizards are easily distinguished from immature Western and Eastern Green Lizards by the number of stripes running down their backs: Balkan Green Lizards have 3 or 5 stripes, while Western and Eastern Green Lizards have either 2 or 4 stripes.
There is an ongoing discussion as to whether Lacerta viridis and Lacerta bilineata are separate species.

1st, 2nd & 3rd photo: A juvenile. Lesvos, Greece, 24 April 2010
4th photo: An adult. Lavrion, Greece, 28 September 2012