title: How to replace colors with textures via Shaders in Unity 3D
body: <p>I have a problem. I tried to search but I can't find what I want. 
  I have a texture. This texture have a blue, green and black colors. They are masks, this is a face texture actually. I want to replace them like blue color will replace with my eyes texture in unity, green color will replace with face texture.. How can I write this shader? I searched but only I find color changing shaders :( Thanks..</p>