We’re not talking about the display resolution, but rather the displays being used. Sony naturally did not specify who are their suppliers, but as it turns out there are two – Truly LCM and Innolux LCM. While OEMs tend to use multiple suppliers, it would seem that in Sony’s case, the different suppliers have provided by different looking displays as you can see in the photos above and below.
To the left is the display supplied by Innolux while the one on the right is from Truly. From the photos it is obvious which display is “better”, which is Truly’s model as the blacks appear to be deeper and overall it feels richer in terms of color reproduction, while Innolux’s model seems “brighter”.
It is unclear if this is a software issue where the Innolux model needs to be recalibrated. It is also unclear as to how many users might have been affected by this issue, but if you’re thinking of picking up the Xperia C5 Ultra and you want to see which brand’s display you got, you can enter *#*#7378423#*#* to access the service menu.