Deep have been facing the exact same issue , I tried contacting the support team but they have been unable to provide any solution so far.. not just black colours , if you use the phone in the dark with low brightness the colours start going greyish? And biggest issue of all time.. put the brightness of the phone at the minimum and then scroll the app drawer, notice the apps which have a black icon and you’ll notice the the icon itself is smudging all over the display as you scroll up and down….
The issue is that right now my phone is barely a month old and I can guarantee you that after a year this display is gonna get worse if there are green line issues, display issues and LCD burning issues right now then what happens at that time?
Nothing really needs to address this issue ASAP and do the right thing