title: Matlab imwrite changed my colour
body: <p>I'm trying to convert some similar images from gif to png.
  You can find two of the pictures here:
  <a href="https://europa.eu/european-union/about-eu/history/1980-1989_en" rel="nofollow noreferrer">https://europa.eu/european-union/about-eu/history/1980-1989_en</a>.
  After converting the first gif (for the year 1981), you can see the background colour is the same as before, white, but for the second gif (for the year 1986), the background colour changed to pink. How to fix it?</p>
  
  <p>Below is my code:</p>
  
  <pre><code>file_in = uigetfile('*.*', 'All Files', 'MultiSelect','on');
  file_out = cellfun(@(x) cat(2, x(1:(length(x)-3)), 'png'),...
     file_in, 'UniformOutput', false); 
  
  for i = 1: length(file_in)    
     [gif,map] = imread (file_in{i});
     imwrite (gif, map, file_out{i}, 'Background', [0 0 0]);
  end
  </code></pre>