title: Replace a particular color inside an image with another color
body: <p>I have one "room" image.</p>
  
  <p>Now, user will click on any particular color suppose blue color in image.</p>
  
  <p>And also user will select replaced color like "black" color.</p>
  
  <p>So, all "blue" color inside the image will be replaced by "black" color.</p>
  
  <p>Any one have idea for how to achieve this in iPhone?</p>
  
  <p>Help is appreciated. </p>