Colour is probably the most subjective test of the bunch because of how we perceive colour. Picking a winner was pretty difficult because the two iPhones were very close. Personally, I like the slightly less saturated colours on the iPhone X but for social media purposes, the more saturated iPhone 8 Plus’ image will definitely look better on more screens. I especially like the blues on the 8 Plus better but I the iPhone X gets more of the other colours right.
In third place, I’d give it to the Samsung Galaxy Note8 with the Mate 10 Pro in last place.
The Mate 10 Pro’s colours were just wildly oversaturated and is even soft around the edges (I’m guessing software bokeh). This, I believe, is because of the Mate 10 Pro’s AI image recognition feature which identified the M&Ms as food and boosted the saturation.