title: C++ | Change color in cv::mat with setTo
body: <p>I have a cv::Mat file with vec3b values. These values are colours from an image. I'd like to change some colours in that image.</p>
  
  <p>I know the setTo() function for normal matrix manipulation, but how do I use it for my Mat file? </p>
  
  <p>I tried something like this:</p>
  
  <pre><code> image = image.setto(Vec3b(0,0,0), image == Vec3b(255,0,0))
  </code></pre>
  
  <p>Thx!</p>