Hello Valerie,
not much of help here, but as you have allready know, I suppose, a juvenile White Wagtail can be excluded by clear and strong olive, brown and yellow tones in the back and wing. Head pattern with dark, blackish crown is also better for Yellow/Citrine than for White.
But further? I havent seen a juvenile Citrine yet, so its one of those threads I learn from, but: according to literature, juvenile Citrines are said to have prominent white wingbars. Your bird looks like the juvenile Yellow Wagtails of ssp flava, that I see in central Europe. Your bird wouldnt stand out among them, with greater coverts are tipped cream-white with a yellowish tinge.
Its hard to be certain, but I think the undertail-coverts have a slight yellow-buffish wash. This can be explainend by reflection of vegetation and or blurred out of focus vegetation, but shouldnt a Citrine have white undertail-coverts?
Conclusion? Does this mean, this is a Yellow Wagtail for me? No, saying, that your bird looks like juvenile flava Yellow Wagtails isnt much of help, as juvenile Yellow and Citrine are very similar according to literature.
Interesting picture. Thanks for sharing!