Grey or Yellow Wagtail

Please would you try and settle a (friendly) family dispute. I live in Redhill, Surrey. On 28th April this year, I saw a wagtail in my garden. Grey Wagtails visit our pond every so often, but this one was a little further away so I couldn't see it so well, spent most of its time on the lawn, seemed to be a little smaller than the greys I've seen, and appeared to have more of a khaki colour on its back rather than grey. I think it was a Yellow Wagtail but my sister (who's definitely more experienced than I) identified it from the photos as a Grey. I'm not yet convinced and would really appreciate a second opinion.

Any comments gratefully appreciated.

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