surface shader homeworld (space) colorize transparent

Hi,

I have a problem regarding a fragment-shader. I tried to port a homeworld shader to unity which is working very nice except one problem remaining.

The teamcolors should only be shown on the transparent areas of the texture. Actually the whole ship is colorized.

Here is the unity part:

 Shader "Kilomoana/s_ship" {
     Properties {
         _MainTex ("Base (RGB)", 2D) = "white" {}
         _SpecSI ("SpecSI (RGB)", 2D) = "white" {}
         _Shininess ("Shininess", Range (0.01, 10)) = 0.078125
         _SpecColor ("Specular Color", Color) = (0.5, 0.5, 0.5, 1)
         _SelfIlluminationBlue("Glow Blue", Range (0, 1)) = 0.5
         _ColorA("Team Color A", Color) = (1,0.8,0,1)
         _ColorB("Team Color B", Color) = (0,0,1,1)
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         LOD 200
         
         CGPROGRAM
         #pragma surface surf BlinnPhong
         sampler2D _MainTex;
         sampler2D _SpecSI;
         float _Shininess;
         float _SelfIlluminationBlue;
         float4 _ColorA;
         float4 _ColorB;
         
         struct Input {
             float2 uv_MainTex;
             float3 worldRefl;
         };
 
         void surf (Input IN, inout SurfaceOutput o)
         {
             // diffuse color
             half4 c  = tex2D (_MainTex, IN.uv_MainTex);
             
             // specular & glow strength
             half4 c2 = tex2D (_SpecSI , IN.uv_MainTex);
 
             // two colors
             float4 teamBaseCol   = (c + 0.5f) * _ColorA + (c - 0.5f);
             float4 teamStripeCol = (c + 0.5f) * _ColorB + (c - 0.5f);
             
             // team color amount is defined by alpha values
             float teamBaseAmount   = 1 - c.a;
             float teamStripeAmount = 1 - c2.a;
 
             // compute final base color
             float4 base = float4(1,1,1,1);
 
             base.rgb = lerp( teamBaseCol.rgb  , c.rgb   , teamBaseAmount   );
             base.rgb = lerp( teamStripeCol.rgb, base.rgb, teamStripeAmount );
     
             half spec     = c2.b;
             half selfIlluBlue = c2.g;
             half selfIlluChangedBlue = selfIlluBlue * _SelfIlluminationBlue;
                         
             o.Gloss    = spec;
             o.Specular = _Shininess;
             
             o.Emission = (selfIlluChangedBlue) * c;
             
             o.Albedo   = lerp( base.rgb, float3(0,0,0), selfIlluChangedBlue);
             o.Alpha    = base.a;
         }
         ENDCG
     } 
     FallBack "Diffuse"
 }
 

This is the original shader:

 static Texture $diffuse
 static Texture $glow
 
 simple base(Texture $diffuse, Texture $glow, Colour $teambase, Colour $teamstripe, Colour $fogColour, Colour $addColour, Colour $shadowColour)
 {
     setCap depthBufferCap true
     setCap gouraudCap true
     setCap cullCap true
     setCap texture0Cap true
     setCap lightingCap true
 
     fillMode solidFill
     cullMode backCull
 
     material ambient   1 1 1 1
     material diffuse   1 1 1 1
     material specular  1 1 1 1
     material shininess 96 96 96 96
     setVertexColour    1 1 1 1
 
     textureBind 0 $diffuse
 //    textureMode    replaceMode
 }
 
 simple light(Texture $diffuse, Texture $glow, Colour $teambase, Colour $teamstripe, Colour $fogColour, Colour $addColour, Colour $shadowColour)
 {
     setCap depthBufferCap true
     setCap gouraudCap true
     setCap cullCap true
     setCap texture0Cap false
     setCap texture1Cap false
     setCap lightingCap true
     setCap blendCap true
 
     srcBlend    destColourBlend
     destBlend    zeroBlend
 
     fillMode solidFill
     cullMode backCull
 
     material ambient   1 1 1 1
     material diffuse   1 1 1 1
     material specular  1 1 1 1
     material shininess 96 96 96 96
     setVertexColour    1 1 1 1
 }
 
 
 simple fog(Texture $diffuse, Texture $glow, Colour $teambase, Colour $teamstripe, Colour $fogColour, Colour $addColour, Colour $shadowColour)
 {
     setCap depthBufferCap true
     setCap gouraudCap true
     setCap blendCap true
     setCap cullCap        true
 
     srcBlend srcAlphaBlend
     destBlend invSrcAlphaBlend
 
     fillMode solidFill
     cullMode backCull
 
     setVertexColour    $fogColour    
 }
 
 compound ship()
 {
     addPass base
     //addPass light
     addPass fog
 }
 

Tinted in a dark gray it already looks nicely:

When tinted in red you can see the wrong effect:

Hope someone could help me out.