title: Unity Shader: Need help creating texture layers that don't affect other layers
body: <p>I'm trying to learn how to write shaders in Unity and am having trouble separating the color and alphas values from affecting the other textures(or layers).</p>
  
  <p>In my shader I have 3 textures of letters (The backgrounds are made transparent in the unity texture settings for each).</p>
  
  <p>I want to have a background color then I need 3 texture/layers on top of the background and be able to change the tint and alpha of each layer without affecting the background or any other layer.</p>
  
  <p>also...</p>
  
  <p>When I multiply the Color by the texture in the surf function, The texture tint changes but also does the transparent background. Why is the transparent backgrounds tint changing when it is transparent?</p>
  
  <pre><code>Properties{
    _Background("BackroundColor", Color) = (1,1,1,1)
    _Color("c1", Color) = (1,1,1,1)
    _Color2("c2", Color) = (1,1,1,1)
    _Color3("c3", Color) = (1,1,1,1)
    _MainTex ("layer1", 2D) = "white" {}
    _MainTex2 ("layer2", 2D) = "white" {}
    _MainTex3 ("layer3", 2D) = "white" {}
  }
  
  SubShader {
     Tags { "RenderType"="Opaque"}
  
          CGPROGRAM
          #pragma surface surf Lambert alpha
          #pragma target 3.0
  
          struct Input {
            float2 uv_MainTex;
            float2 uv2_MainTex2;
            float2 uv3_MainTex3;
          };
  
          sampler2D _MainTex; 
          sampler2D _MainTex2; 
          sampler2D _MainTex3; 
          float4 _Background;
          float4 _Color;
          float4 _Color2;
          float4 _Color3;
  
          void surf (Input IN, inout SurfaceOutput o) {
            o.Albedo = _Background * (tex2D (_MainTex, IN.uv_MainTex).rgb*_Color) * (tex2D (_MainTex2, IN.uv2_MainTex2).rgb*_Color2) * (tex2D (_MainTex3, IN.uv3_MainTex3).rgb*_Color3);
  
            o.Alpha = _Color.a * _Color2.a * _Color3.a;
  
          }
          ENDCG
  }
  Fallback "Diffuse"
  </code></pre>