I think the color of the bird can be explained by the fact it was taken in the evening. The sun at that time tends to turn even the greyest birds brown.
I don't think the size of the bird is mentioned, but it is apparent from the photo that it is not the sizeof a prinia. I think only the Prinia's behaviour was referred to.
Upcher`s in Saudia Arabia always had the same wagging tail habit, though I have seen Olive-Tree and Olivaceous do it too.
No point in me re-iterating plumage features that have already been pointd out. The lower mandible looks orange..can`t remember if that is good for Upcher's or not though, but the structure of the bill dosn't look big enough for Olive-tree, but might fall within the range of Upcher's or Olivaceous.
However, I guess this is an Upcher's, certainly a 'hippolais' and not any other family, such as acro's, or scrub warblers..certainly way too big for the latter.
Nice pics once again