Quantization on an RGB Image

I'm having issues with this code on RGB images. I'm trying to use 2D-DCT and quantization to compress an image. My code works on gray images and works if I just transpose the RGB image from one matrix to another. The image comes out dark, and I am at a loss of what the problem is. See examples and code below

Original

Processed

Code

clc
close all

image = imread('picture.jpg');
p=1;

%check if matrix is divisible by 8
if (rem(size(image,1),8) ~= 0)
    disp("width not divisible by 8 croping image");
    imagew = size(image,1) - rem(size(image,1),8);
    image = image(1:imagew,1:size(image,2),1:size(image,3));
end
if (rem(size(image,2),8) ~= 0)
    disp("heigth not divisible by 8 croping image");
    imageh = size(image,2) - rem(size(image,2),8);
    image = image(1:size(image,1),1:imageh,1:size(image,3));
end

%gray scale
%  r=image(:,:,1);
%  g=image(:,:,2);
%  b=image(:,:,3);
%  original = 0.2126*r+0.7152*g+0.0722*b;
%  original = uint8(original);

%color
original = uint8(image);

figure(1)
imshow(original, []);

rows = (size(original,1));
columns = (size(original,2));
bRow = ceil(size(original,1)/(size(original,1)/8));
bCol = ceil(size(original,2)/(size(original,2)/8));
Q = p*8./hilb(8);

processed = uint8(zeros(rows,columns,(size(original,3))));

for z = 1:size(original,3)
    for y = 0:(size(original,1)/8) - 1 
        for x = 0:(size(original,2)/8) - 1
            x0 = x*bCol+1;
            y0 = y*bRow+1;
            x1 = min(x0+bCol-1, columns); 
            y1 = min(y0+bRow-1, rows);

              xb = original(y0:y1,x0:x1,z);

              dct2xb = round(dct2(xb));
              Xd = double(xb);
              Xc = Xd - 128;
              Yq = round(dct2xb ./ Q);
              idct2xb = idct2(Yq);

             processed(y0:y1,x0:x1,z) = uint8(idct2xb);
            % processed(y0:y1,x0:x1,z) = uint8(xb);

          end
      end
  end

figure(2)
imshow(processed, []);

Full disclosure, yes this is homework.