Shine a flashlight into the Apple Logo in the display are you able to see the faint image of your desktop and its icons? If you can only your backlight logic needs to be looked at.
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=== Update (04/21/2018) ===
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At this point, I think you'll need to pop the bottom cover off and inspect the display cable connection. Review the this IFIXIT guide: [https://www.ifixit.com/Guide/MacBook+Pro+13-Inch+Retina+Display+Early+2015+Display+Assembly+Replacement/45135]. After disconnecting the battery jump down to Step11. Take some detailed pictures and post them here for us to see.
Shine a flashlight into the Apple Logo in the display are you able to see the faint image of your desktop and its icons? If you can only your backlight logic needs to be looked at.