Shader: combine two textures and add transparency

Hi,

i’m new to Unity and shaders, and I tried really a lot of things to modify/create a shader for my needs.
I’m trying to make a “page shine through effect”, that means I have an image/texture where I need to add some white on top (I really don’t know how to explain it), to get it looking less strong. Now I used a second white texture with alpha 0.9 or something to just let 10% of the main textures colors “shine through”.
I got that working so far, but I need to fade this “page” in and out, that means I need to add an alpha/transparency for the whole thing.

Here is what I came up with until now, any help/suggestions are highly appreciated!
Thx in advance!

Shader "PageFlip/Page3"
{
	Properties 
	{
		_Color ("Main Color", Color) = (1,1,1,1)
		_MainTex ("Base (RGB) Trans (A)", 2D) = "white" {} 
		_BlendTex ("Blend (RGB)", 2D) = "white"
	}
	SubShader 
	{
		Tags { "Queue"="Geometry-9" "IgnoreProjector"="True" "RenderType"="Transparent" }
		Lighting Off
        ZTest GEqual
		LOD 200
		//Blend SrcAlpha OneMinusSrcAlpha
		
		CGPROGRAM
		#pragma surface surf Lambert
		// add "alpha" to pragma to turn on alpha
		
		sampler2D _MainTex;
		fixed4 _Color;
		
		struct Input {
			float2 uv_MainTex;
		};
		
		void surf (Input IN, inout SurfaceOutput o) {
			fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
			o.Albedo = c.rgb;
			o.Alpha = c.a;
		}
		ENDCG
		
		Pass {
            SetTexture [_MainTex] 
            SetTexture [_BlendTex] {
                constantColor (0, 0, 0, 0.9) // last value is blend opacity
                combine texture lerp (constant) previous
            }
        }
	}
	
	Fallback "Transparent/VertexLit"
}

If I got you right then something like this will do. You can translate between _MainTex and _BlendTex using _BlendAlpha parameter changing it from 0 to 1. Also you can change the whole objects’s transparency using _Color alpha due to blending.

Shader "PageFlip/Page3"
{
    Properties 
    {
       _Color ("Main Color", Color) = (1,1,1,1)
       _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {} 
       _BlendTex ("Blend (RGB)", 2D) = "white"
       _BlendAlpha ("Blend Alpha", float) = 0
    }
    SubShader 
    {
       Tags { "Queue"="Geometry-9" "IgnoreProjector"="True" "RenderType"="Transparent" }
       Lighting Off
       LOD 200
       Blend SrcAlpha OneMinusSrcAlpha
 
       CGPROGRAM
       #pragma surface surf Lambert
 
       fixed4 _Color;
       sampler2D _MainTex;
       sampler2D _BlendTex;
       float _BlendAlpha;
 
       struct Input {
         float2 uv_MainTex;
       };
 
       void surf (Input IN, inout SurfaceOutput o) {
         fixed4 c = ( ( 1 - _BlendAlpha ) * tex2D( _MainTex, IN.uv_MainTex ) + _BlendAlpha * tex2D( _BlendTex, IN.uv_MainTex ) ) * _Color;
         o.Albedo = c.rgb;
         o.Alpha = c.a;
       }
       ENDCG
    }
 
    Fallback "Transparent/VertexLit"
}