How to save an image without reverse the black/white in the image ??

I want to extract the color region from image , this works fine but the problem is in the save part . When I save the image , it converts the black to white and vise versa but I do not know why . This is the image :

and this is how it saves it :

matlab code:

I = imread('./img/bfly.png');

[Iu,ia,iu] = unique(reshape(I,[],3),'rows');
counts = accumarray(iu,1);
[counts,sortinds] = sort(counts,'descend');

N = 10;
largestLabels = sortinds(1:N);

for i= 1:6
    mapi = reshape(iu == largestLabels(i),size(I,1),size(I,2));

      L = bwlabel(mapi);
      figure,imshow(L ==0)

      im_name=strcat('image',num2str(i),'.png'); 

      imwrite(mapi,im_name)
  end