Set different color for each face

Hi everyone, I try to color the faces of my hexagon. My problem it colors the hexagon vertices and then interpolate the color.. I would like to color each face with a different color and not blend them.

My code:

 using UnityEngine;
 using System.Collections;
 
 public class SetCubeColor : MonoBehaviour {
     public Shader shaders;
     // Use this for initialization
     void Start()
     {
       
 
         Mesh mesh = GetComponent<MeshFilter>().mesh;
         GetComponent<MeshRenderer>().material = new Material(shaders);
         Vector3[] vertices = mesh.vertices;
         Debug.Log("taille vercitces, MMMMMMMMMMMMMMMMMM" + mesh.colors.Length + "    " + mesh.colors32.Length);
         Color[] colors = new Color[vertices.Length];
 
         int i = 0;
         while (i < vertices.Length)
         {
             colors[i] = Color.Lerp(Color.blue, Color.green, vertices[i].y);
             i++;
         }
         mesh.colors = colors;
     }
 
 }
 

The shader code:

 Shader "VertexColour"
 {
     SubShader{
         Pass{
         Fog{ Mode Off }
         CGPROGRAM
 
 #pragma vertex vert
 #pragma fragment frag
 
         // vertex input: position, color
     struct appdata {
         float4 vertex : POSITION;
         fixed4 color : COLOR;
     };
 
     struct v2f {
         float4 pos : SV_POSITION;
         fixed4 color : COLOR;
     };
 
     v2f vert(appdata v) {
         v2f o;
         o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
         o.color = v.color;
         return o;
     }
 
     fixed4 frag(v2f i) : SV_Target{ return i.color; }
         ENDCG
     }
     }
 }
 

Current rendering :

I simply want to colorate each face of the hexagon with a different color.

Thanks in advance.