The "green" part of the name refers to the light green colouration of the foliage not the flower. I find that some of the flowers are blue but often they are very pale or white like this one. The plant looks like a poor specimen of Veronica persica until you look more closely at the seeds. The two seeds of V. persica have axes pointing away from each other making an obtuse angle but in V. agrestis the axis is parallel. In addition the leaves are usually alternate except at the bottom of the flowering stem.