concatenate multiple 2D arrays to a 3D array for an image file.

I have an image file (.jpg) that I am trying to display on a graph side by side with the original of the image. After splitting the 3D color array into 3 2D arrays (RGB), I made an edit to the file, and tried to concatenate the layers back into a 3D matrix, but instead it's displaying the images side by side. How do I get the file to display the image with all 3 2D colormaps on top of each other instead of displaying them side by side?

[WhiteImg, colorMap] = imread('OrigImg.jpg');
    Rlayer = ...
        WhiteImg( :, :, 1);
    Glayer = ...
        WhiteImg( :, :, 2);
    Blayer = ...
        WhiteImg( :, :, 3);
    
    % FIND WHITE PIXELS
    logArray = ...
        (Rlayer > 220) & (Glayer > 220) & (Blayer > 220);
    intensity( :, :) =  ...
        uint8(mean([Rlayer, Glayer, Blayer], 3));
    
    % INDEX NEW RGB LAYERS
    Rnew = ...
        intensity(:, :);
    Gnew = ...
        intensity(:, :);
    Bnew = ...
        intensity(:, :);
    
    % SWAP WHITE FOR RED COLOR
    Rnew(logArray) = 255;
    Gnew(logArray) = 0;
    Bnew(logArray) = 0;
    
    % CONCAT
    RedImg = ...
        cat(3, Rnew, Gnew, Bnew);
    
    % PLOTS
    figure
        blockPlots = subplot(1, 2, 1);
            image(WhiteImg);
            axis image
            axis off
        blockPlots = subplot(1, 2, 2);
            image(RedImg);
            axis image
            axis off

Answer 1

[Kevin Holly]

[WhiteImg, colorMap] = imread('peppers.png');
    Rlayer = ...
        WhiteImg( :, :, 1);
    Glayer = ...
        WhiteImg( :, :, 2);
    Blayer = ...
        WhiteImg( :, :, 3);
    
    % FIND WHITE PIXELS
    logArray = ...
        (Rlayer > 220) & (Glayer > 220) & (Blayer > 220);
    intensity = uint8(mean(WhiteImg,3));
    
   
    % INDEX NEW RGB LAYERS
    Rnew = intensity;
    Gnew = intensity;
    Bnew = intensity;
    
    % SWAP WHITE FOR RED COLOR
    Rnew(logArray) = 255;
    Gnew(logArray) = 0;
    Bnew(logArray) = 0;

    
    % CONCAT
    RedImg = WhiteImg;
    RedImg(:,:,1) = Rnew;
    RedImg(:,:,2) = Gnew;
    RedImg(:,:,3) = Bnew;
    

    % PLOTS
    figure
        blockPlots = subplot(1, 2, 1);
            image(WhiteImg);
            axis image
            axis off
        blockPlots = subplot(1, 2, 2);
            image(RedImg);
            axis image
            axis off

To make them closer together:

            figure
            imshowpair(WhiteImg,RedImg,"montage")