I was skeptical, but indeed it seems that you have liquid in there!
If you're lucky, it will dry out a bit over time.
In my opinion, it is not worth replacing the screen unless it fails - which may happen if liquid also seeped onto the board of the screen.
I think liquid either sipped through the clutch, or through a weakness in the black gasket at the bottom left corner of the screen.
If there is no weakness in that corner, and you suspect it went in through the clutch cover, you may want to remove the screen, and clutch cover, and have a look in case some liquid is still sitting in there - which you'll need to dry out. I would recommend using a q-tip dipped in isopropyl alcohol, 90% or higher concentration. The alcohol will "dilute" the water and evaporate it, and clean mineral residue that can cause corrosion,
[guide|45135|Here's a guide for removing the screen assembly]. [https://www.youtube.com/watch?v=kyrljFnByPY&t=18s|And here's a video]. Next you will want to remove the clutch cover (black half-tube). [http://www.insidemylaptop.com/13-macbook-pro-retina-fixing-no-video-issue-by-replacing-display-cable/|This guide can tell you how].