I photographed this bird on high ground in Nova Scotia near Halifax. It does not appear to be any North American Warbler. It comes across as a weird cross between a Cerulean Warbler and a Palm Warbler.
It is a warbler, looks like some kind of Setophaga. My best guess is Yellow-rumped, but there is no yellow on it. Or a dull female Cape May, but this bird has back streaks. Do you have any other angles?
I'm pretty sure it's not a Sylvia or other European warbler. It looks very similar to an adult male Cerulean, and Cerulean has been spotted in Halifax before.
I haven't seen one, but I naturally wondered about an immature Cerulean - my book says they're similar to females, meaning they have faint or no breast streaking, and may show an eye ring. But they should be "dull" and faintly yellowish. Can't see a single feather in the photo that's not crisp and bright.
The photo is quite heavily oversaturated, which prevents accurate perception of the colours and thus of ID. Do you have an unedited version of the photo? - or is this how it came out of the camera? If the latter, and if you wish to use the camera to get IDs, you might consider adjusting its settings to change the colour tone to something more realistic/neutral - if this is how the photo came out of the camera, the colour tone is presumably set currently on 'vivid' or somesuch.
I don't see anything in it to suggest palm warbler, and not much to suggest cerulean warbler (underparts in particular are wrong). Given the fact that (I suspect) the colours here are not the colours of the actual bird, bay-breasted warbler seems a good option, e.g. chestnut on underparts, prominent pale side to hindneck.
Interesting one. When I first opened the pic my mind went straight to fem Bay-breasted, and I did not for one moment register the slightest hint of blue... that's not to suggest I'm some kind of expert, far from it, I'm just familiar with the species ....and there's no denying that when one zooms in on the mantle in isolation it does look very blue.
Presumably if you are familiar enough with a bird, your brain jumps to your mental memory of it, and filters the apparent colour artefacts that shouldn't be there, but if its an unfamiliar bird one may perceive these colours as true to life.
I guess this could be problematic in two respects- one might overlook a subtle difference and miss something different from the norm, because we are not expecting it.... or one may jump to the wrong conclusions if not familiar enough, especially in poor images.
Either way, a good lesson in how colour perception of images is fraut with difficulty, especially when also factoring in the influence of one's screen/device!