ciede2000 | CIEDE2000 color difference algorithm

I am making a program where I want to take an image and reduce its color palette to a preset palette of 60 colors, and then add a dithering effect. This seems to involve two things:

• A color distance algorithm that goes through each pixel, gets its color, and then changes it to the color closest to it in the palette so that that image doesn't have colors that are not contained in the palette.
• A dithering algorithm that goes through the color of each pixel and diffuses the difference between the original color and the new palette color chosen across the surrounding pixels.

After reading about color difference, I figured I would use either the CIE94 or CIEDE2000 algorithm for finding the closest color from my list. I also decided to use the fairly common Floyd–Steinberg dithering algorithm for the dithering effect.

Over the past 2 days I have written my own versions of these algorithms, pulled other versions of them from examples on the internet, tried them both first in Java and now C#, and pretty much every single time the output image has the same issue. Some parts of it look perfectly fine, have the correct colors, and are dithered properly, but then other parts (and sometimes the entire image) end up way too bright, are completely white, or all blur together. Usually darker images or darker parts of images turn out fine, but any part that is bright or has lighter colors at all gets turned up way brighter. Here is an example of an input and output image with these issues:

Input:

]3

Output:

I do have one idea for what may be causing this. When a pixel is sent through the "nearest color" function, I have it output its RGB values and it seems like some of them have their R value (and potentially other values??) pushed way higher than they should be, and even sometimes over 255 as shown in the screenshot. This does NOT happen for the earliest pixels in the image, only for ones that are multiple pixels in already and are already somewhat bright. This leads me to believe it is the dithering/error algorithm doing this, and not the color conversion or color difference algorithms. If that is the issue, then how would I go about fixing that?

Here's the relevant code and functions I'm using. At this point it's a mix of stuff I wrote and stuff I've found in libraries or other StackOverflow posts. I believe the main dithering algorithm and C3 class are copied basically directly from this Github page (and changed to work with C#, obviously)