system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does contrast increase/decrease when looking at a monitor from an angle?
gpt
LCD work by shining a bright white light (actually a combination of every color, ever see a prism?) from behind the display, then controlling how much of each color can pass through each pixel.

This is achieved through multiple stacked layers which have these light and color filters embedded for each pixel. When a pixel is white, it allows most of the light to pass through. When it's black, most of that light is being absorbed or reflected back into the monitor.

If that light moves sideways, it bleeds to neighboring pixels and lowers contrast by mixing different colors and blurring edges. This is ultimately stopped by putting "prism" walls around each pixel. When viewed head-on, the walls look the same as the pixels. From the side, you see the different mix of color the walls are redirecting at that angle. As you lower your view angle, you also see more of the walls and less of the pixels. This is why active parts of the display change color when viewed from the side, and why black sections mostly look the same.

Edit: Just wanted to add that with older and large format displays, discoloration was instead mostly a result of polarization angle. However, modern high density formats required a shift to extremely thin layers or a curved format to prevent this from occuring at either side of a display you were looking at head-on. Thinner layers introduced problems related to irregularities in thickness, which are generally solved by optical separation.