How to apply a color to the second texture in this shader?

This a modification of the built in Transparent Diffuse shader of Unity. I've been trying to set the Color2 as the color of the Tex2. How can I do that?

 Shader "Transparent/Diffuse2" {
 Properties {
     _Color ("Main Color", Color) = (1,1,1,1)
     _Color2 ("Main Color2", Color) = (1,1,1,1)
     _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
     _Tex2 ("B", 2D) = "white" {}
 }
 
 SubShader {
     Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
     LOD 200
 
 Pass {
         Material {
                 Diffuse [_Tex2]
                 Diffuse [_MainTex]
                 
             }
             
             
             // Apply base texture
             SetTexture [_MainTex] {
                 combine texture
             }
             // Blend in the alpha texture using the lerp operator
             SetTexture [_Tex2] {
                 //constantColor [_Color2]
                 combine texture lerp (texture) previous
             }
         }
 CGPROGRAM
 #pragma surface surf Lambert alpha
 
 sampler2D _MainTex;
 sampler2D _Tex2;
 fixed4 _Color;
 fixed4 _Color2;
 
 
 
 
 struct Input {
     float2 uv_MainTex;
     float2 uv_Tex2;
 };
 
 void surf (Input IN, inout SurfaceOutput o) {
     
     
     fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
     fixed4 b = tex2D(_Tex2, IN.uv_Tex2) * _Color2;
     
     o.Albedo = c.rgb;
     o.Alpha = c.a;
 }
 ENDCG
 }
 
 Fallback "Transparent/VertexLit"
 }
 

My objective is to have a texture with alpha channel, which has its own color, overlaying an opaque texture, which has its own color. Sounds simple, but I couldn't find a single shader that does that.