I don't understand how come the colors and details got all messed up in the rendered vid. Any help please?
Neither do we. Seriously, you need to provide much more info about your project and screenshots of the timeline and settings used.
Here is a picture of my timeline. Thirdparty plugins used: twitch, optical flares, element 3d. The buildings in the background was rotoscoped in photoshop and added in as a layer. Since some buildings became transparent as I accidentally erased them a bit, I added a new black solid layer beneath it for a more sturdy look.
If you need, I could upload the entire project file.
This could be a gamma shift. We cant tell you how to fix it if you don't tell us what your render settings are and how your color management is setup.
This is a screenshot of your post with videos stopped at the about the same time. I checked the screenshot in Photoshop and there was almost no difference between the images. YouTube compression may account for that.
This is one shot laid over the other with the top copy set to difference. If the pixels were an exact match the image would be completely black. There are slight differences that you have to look closely to see. These could be just the difference in rendering codecs but without knowing your exact settings I can't help any more.