I have a specular outline shader that I want to be used on all opaque meshes of the scene whenever a specific camera renders. The shader is working properly when it is manually applied to some material. The shader is as follows:

Shader "Custom/Outline" {
Properties {
    _Color ("Main Color", Color) = (.5,.5,.5,1)
    _OutlineColor ("Outline Color", Color) = (1,0.5,0,1)
    _Outline ("Outline width", Range (0.0, 0.1)) = .05
    _SpecColor ("Specular Color", Color) = (0.5, 0.5, 0.5, 1)
    _Shininess ("Shininess", Range (0.03, 1)) = 0.078125
    _MainTex ("Base (RGB) Gloss (A)", 2D) = "white" {}
}

SubShader {
    Tags { "Queue"="Overlay" "RenderType"="Opaque" }
    Pass {
        Name "OUTLINE"
        Tags { "LightMode" = "Always" }

        Cull Off
        ZWrite Off
        // Uncomment to show outline always.
        //ZTest Always

        CGPROGRAM
        #pragma target 3.0
        #pragma vertex vert
        #pragma fragment frag

        #include "UnityCG.cginc" 

        struct appdata {
            float4 vertex : POSITION;
            float3 normal : NORMAL;
        };

        struct v2f
        {
            float4 pos : POSITION;
            float4 color : COLOR;
        };

        float _Outline;
        float4 _OutlineColor;

        v2f vert(appdata v) {
            // just make a copy of incoming vertex data but scaled according to normal direction
            v2f o;
            o.pos = mul(UNITY_MATRIX_MVP, v.vertex);

            float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);
            float2 offset = TransformViewToProjection(norm.xy);

            o.pos.xy += offset * o.pos.z * _Outline;
            o.color = _OutlineColor;
            return o;
        }

        float4 frag(v2f fromVert) : COLOR {
            return fromVert.color;
        }
        ENDCG
    }
    UsePass "Specular/FORWARD"
}

FallBack "Specular"
}

The camera used fot the effect has just a script component which setups the shader replacement:

using UnityEngine;
using System.Collections;

public class DetectiveEffect : MonoBehaviour {

    public Shader EffectShader;

    // Use this for initialization
    void Start () {
        this.camera.SetReplacementShader(EffectShader, "RenderType=Opaque");
    }

    // Update is called once per frame
    void Update () {

    }
}

Unfortunately, whenever I use this camera I just see the background color. Any ideas?