[Cg] Lighting a projected alpha-blended decal

Managed to get a functional alpha projector, now I'm trying to get it lit. Problem is, it seems the projection only does one light at a time, meaning the decal is entirely affected by the light colour. The decal in the screenshot is supposed to be white and magenta, the blue light being a relatively small point light on the other side of the screen.

The code:

 Shader "Custom/Projector Decal" {
          Properties {
              _MainTex ("Main Texture", 2D) = "grey" {}
              _Mask ("Alpha Mask", 2D) = "white" {}
              _Color ("Colour", Color) = (1,1,1,1)
          }
          SubShader {
          
               Tags { "Queue"="Transparent" "IgnoreProjector"="False" "RenderType"="Transparent" }
                 Cull Off
              Offset -1, -1 
              Blend Zero SrcAlpha
              
              CGPROGRAM
              #include "UnityCG.cginc"
              #pragma surface surf Decal alpha noambient addshadow vertex:fProjUVs
              
              sampler2D _MainTex;
              half4 _Color;
              uniform float4x4 unity_Projector;
              
              struct Input {
                  float2 uv_MainTex;
                  float4 projPos : TEXCOORD0;
              };
 
             void fProjUVs (inout appdata_full v, out Input o) {
                 UNITY_INITIALIZE_OUTPUT (Input, o);
                 o.projPos = mul (unity_Projector, v.vertex);
             }
              
              void surf (Input IN, inout SurfaceOutput o) {
                  if (IN.projPos.z > 0) {
                     half4 c = tex2D (_MainTex, IN.projPos.xy / IN.projPos.w) * _Color;
                     o.Albedo = c.rgb;
                     o.Alpha = c.a * (1 - IN.projPos.z) * _Color.a;
                  }
              }
              
              half4 LightingDecal (SurfaceOutput s, half3 lightDir, half atten) {
                  half4 c;
                  c.rgb = (s.Albedo * (_LightColor0 * atten));
                  c.a = s.Alpha;
                  return c;
              }
              ENDCG
          }
          FallBack "Diffuse"
      }