Why does my screen colour turn a bit light when I turn my brightness up and then adjust back a few seconds later? Also, why can I see a stain/mark that seems to stay forever on my MacBook Pro?

Recently, over a few weeks I have been experiencing a few issues when using my mac and these problems are usually linked with the display. I have decided to post on the forum to see if I can get any answers/solutions to them or perhaps receive insight to how/why these problems exist. I have already booked a Genius Bar appointment next Saturday however, I was wondering if anyone knows what is causing these problems to exist.

1) Every time I take my laptop out of my bag and boot it up, yellow patches/lines form across the left/right side edge of the MacBook. When working on a flat surface, these yellow marks slowly disappear and fade. Despite the surface I am on or whenever I am working, there will always be "feinter" yellow patches across the screen, particularly further in, displaying what seems to look like a smaller outline of the larger screen. Here are some images.

Image of the yellow mark along the edge. (this time it was on the right hand side edge of my mac)

When I use a white wallpaper to examine the "left over" or always visible "feint" yellow patches on my mac, you can see some spots, like discolouration of the display. It seems to have a pinkish colour near the left and moving on to a more yellow shade along the right.

2) When I turn my brightness down to zero, or when my computer is turned off and there is a source of light behind me, particularly sunlight, there appears to be a patch/stain which occurs near the middle of the screen. It looks similar to something I saw on the internet called staingate, but not as apparent/worse as the images on staingate. When I try to remove these marks using water, they continue to stay there and don't disappear.

3) This doesn't occur all the time but sometimes, when I adjust my brightness from 0 to max, it sometimes displays a lighter colour, but then adjusts back to normal after a few seconds. Not too big of an issue but could still potentially be a problem.

If anyone could tell me the causes of these problems outlined above and provide possible solutions to them, that would be great but please do reference the problems by numbers. I have Applecare for my mac which expires dec. 27th 2020 or something.