Objects with custom shaders cast grayscale shadows when lightmapped

Unity 5 seems to be able to calculate colored shadows from standart shader and legacy shaders.

What should I do to make my custom shader to cast colored shadows?

My shader:

 Shader "Opaque/Lightmap"  
 {
     Properties 
   {
         _MainTex ("Base (RGB)", 2D)     = "white" {}
     }
     
     SubShader 
   {
         Tags { "Queue" = "Geometry" "RenderType" = "Opaque" }
         LOD 100
         
         Pass
         {   
             Name "FORWARD"
             Tags { "LIGHTMODE"="ForwardBase" "SHADOWSUPPORT"="false" "RenderType"="Opaque" }
             
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma fragmentoption ARB_precision_hint_fastest
             #pragma exclude_renderers d3d11_9x d3d11
             #pragma multi_compile_fog
             #pragma multi_compile LIGHTMAP_OFF LIGHTMAP_ON
             
             #include "UnityCG.cginc"
             
             sampler2D   _MainTex;
             
             struct appdata 
             {
                 float4 vertex : POSITION;
                 half2 texcoord   : TEXCOORD0;
                 half2 texcoord1  : TEXCOORD1;
             };
     
             struct v2f {
                 float4 pos : SV_POSITION;
                 half2 uv : TEXCOORD0;
                 half2 lightmapuv : TEXCOORD1;
                 UNITY_FOG_COORDS(2)
             };
     
             v2f vert (appdata v) 
             {
                 v2f o;
                 o.pos = mul( UNITY_MATRIX_MVP, v.vertex );
                 o.uv = v.texcoord;
                 o.lightmapuv = v.texcoord1.xy * unity_LightmapST.xy + unity_LightmapST.zw;
                 
                 UNITY_TRANSFER_FOG(o,o.pos);
                 return o;
             }
     
             fixed4 frag (v2f i) : COLOR
             {
                 fixed4 color = tex2D(_MainTex, i.uv);
                 
                 #ifndef LIGHTMAP_OFF
                 fixed3 lightMap = DecodeLightmap(UNITY_SAMPLE_TEX2D(unity_Lightmap, i.lightmapuv));
                 color.rgb *= lightMap;
                 #endif
                 
                 UNITY_APPLY_FOG(i.fogCoord, color);
                 return color;
             }
             ENDCG
         } 
     }
 }