shader Transparency

Hello all I found a wonderful shader that mixes three colors but I need alpha transparency to work for the .png textures I have searched and tried to code no avail

Any Ideas

     Properties
     {
         _MainTex("Main Tex", 2D) = "tranparent" {}
         _Color("Color", Color) = (1.0, 1.0, 1.0, .0)
         _Color1("Color 1", Color) = (1.0, 0.5, 0.5, .0)
         _Color2("Color 2", Color) = (0.5, 0.5, 1.0, .0)
         _Rim("Rim", Float) = 1.0
         _Shift("Shift", Float) = 1.0
     }
 
     SubShader
     {
         Tags
         {
             "Queue" = "Geometry"
             "PreviewType" = "Sphere"
             "DisableBatching" = "True"
         }
 
         Pass
         {
             CGPROGRAM
             #pragma vertex Vert
             #pragma fragment Frag
 
             sampler2D _MainTex;
             float4    _Color;
             float4    _Color1;
             float4    _Color2;
             float     _Rim;
             float     _Shift;
 
             struct a2v
             {
                 float4 vertex    : POSITION;
                 float2 texcoord0 : TEXCOORD0;
                 float3 normal    : NORMAL;
                 float4 color     : COLOR;
                 
             };
 
             struct v2f
             {
                 float4 vertex : SV_POSITION;
                 float2 uv     : TEXCOORD0;
                 float3 normal : TEXCOORD1;
                 float4 color  : COLOR;
             };
 
             struct f2g
             {
                 float4 color : SV_TARGET;
             };
 
             void Vert(a2v i, out v2f o)
             {
                 o.vertex = UnityObjectToClipPos(i.vertex);
                 o.uv     = i.texcoord0;
                 o.normal = mul((float3x3)UNITY_MATRIX_IT_MV, i.normal);
                 o.color  = i.color * _Color;
                 
             }
 
             void Frag(v2f i, out f2g o)
             {
                 float rim = _Shift - pow(saturate(1.0f - normalize(i.normal).z), _Rim);
 
                 o.color = tex2D(_MainTex, i.uv) * lerp(_Color1, _Color2, rim) * i.color;
             }
             ENDCG
         } // Pass
     } // SubShader

Thanks !

~be