How do I change specific locations in an image to black?

My code is supposed to find the differences between two images and create a new image that indicates all these differences in black. Currently I have

%image1 and image2 are the two images to compare
  %creates a mask of the differences imgMatrix1 and imgMatrix2 are the n by m by 3 rgb matrices
  equalityTest=imgMatrix1==imgMatrix2;

    %starts with a black image
    newImageMap=uint8(zeros(a,b,c));

    %turns all the identical spaces white
    newImageMap(equalityTest)=255;

    imwrite(newImageMap,newFileName);
  end

Why is this code returning an image that has color in the correct spots but the color is cyan and not black?

Answer 1

[Image Analyst]

You did it wrong. You should start with the original image and set all differences to black:

% Starts with original image
newImageMap = imgMatrix1; % or imgMatrix2 - it doesn't matter.
% Turns all the different pixels black.
newImageMap(equalityTest) = 0;
% Pixels with non-black color match perfectly in all color channels.
% This will probably happen in computer graphics only, not camera images.

[Bob]

The pattern is coming out cyan instead of black. I'm using newImageMap(~equalityMap)=0; because the map is true for pixels that are equal. How can I get Matlab to zero all the layers?

Edit: So the differences in the test case I'm running with only affects the red value in the pixels which are different. How do I get the green and blue to change along with the red?

[Image Analyst]

Bob, see the full blown demo (test2.m) I wrote for you below in blue. If it does what you expect, then can you mark the answer as Accepted?