What's wrong with the color in the top screen?

I've owned my DSi XL for about 5 years now, and now that i've started repairing some of my devices, I figured I would move on to this one. Unfortunately, I cannot find a previous instance of this problem, so here we go.

About a year ago, I was jogging to get to school on time, and had my DSi XL in my pocket. When I got to school, I pulled it out, and the upper screen was acting strange. The colors are all messed up, with blues often dulling out into greyer colors, or just as close to black as a blue can get and still be blue, whites becoming ambers, yellows and blues that are not mixes becoming green, etc. If memory of light serves, there's probably something wrong with my blue, but if so, what is it, and how do I fix it? If not, what could it be, and how do I fix it? I will try to add pictures later, I do not have any at the moment of writing this.

EDIT:

Here's the pictures, as promised. Please pardon the shoddy camera work.

Here's (mostly) what the screen is supposed to look like,playing a game like pokemon black and white. This is it playing on my DS Lite, and the only problem with the screen is a black line barely noticeable in this picture.

Here's what can be seen on the DSI XL. The difference is notable.