Unity 5 standard shader support for vertex colors?

You can get vertex colors to work with the standard shader (PBR stuff) by making a new Shader. Add vertex:vert to the pragma line in the CGPROGRAM block. You can then add a vertex function to get the vertex color, and then pass that into the surface function to use for the albedo:

 Shader "Custom/StandardVertex" {
     Properties {
         _Color ("Color", Color) = (1,1,1,1)
         _MainTex ("Albedo (RGB)", 2D) = "white" {}
         _Glossiness ("Smoothness", Range(0,1)) = 0.5
         _Metallic ("Metallic", Range(0,1)) = 0.0
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         LOD 200
         
         CGPROGRAM
         #pragma surface surf Standard vertex:vert fullforwardshadows
         #pragma target 3.0
         struct Input {
             float2 uv_MainTex;
             float3 vertexColor; // Vertex color stored here by vert() method
         };
         
         struct v2f {
           float4 pos : SV_POSITION;
           fixed4 color : COLOR;
         };
 
         void vert (inout appdata_full v, out Input o)
         {
             UNITY_INITIALIZE_OUTPUT(Input,o);
             o.vertexColor = v.color; // Save the Vertex Color in the Input for the surf() method
         }
 
         sampler2D _MainTex;
 
         half _Glossiness;
         half _Metallic;
         fixed4 _Color;
 
         void surf (Input IN, inout SurfaceOutputStandard o) 
         {
             // Albedo comes from a texture tinted by color
             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
             o.Albedo = c.rgb * IN.vertexColor; // Combine normal color with the vertex color
             // Metallic and smoothness come from slider variables
             o.Metallic = _Metallic;
             o.Smoothness = _Glossiness;
             o.Alpha = c.a;
         }
         ENDCG
     } 
     FallBack "Diffuse"
 }
 

The full Standard Shader is a big can of worms. Not sure how any of it works at the moment so I can't include this yet.

If anyone is still looking for standard shader with such functionality you should check out this thread: http://forum.unity3d.com/threads/standard-shader-with-vertex-colors.316529/