SetConstantBuffer.cs

using UnityEngine;
using UnityEngine.Rendering;
using Unity.Mathematics;

[RequireComponent(typeof(Camera))]
public class Draw : MonoBehaviour
{
    [SerializeField] public Mesh Mesh;
    [SerializeField] public Material Material;
    private Camera mainCamera;
    private Matrix4x4[] matrices;
    private ComputeBuffer buffer;

    unsafe void Start()
    {
        matrices = new Matrix4x4[1023];
        for (int i = 0; i < matrices.Length; i++)
        {
            matrices[i] = Matrix4x4.identity;
            matrices[i].m03 = i * 0.1f;
            matrices[i].m23 = 50f;
        }
        mainCamera = GetComponent<Camera>();
        buffer = new ComputeBuffer(1023, sizeof(float4), ComputeBufferType.Constant);
        var cols = new float4[matrices.Length];
        for (int i = 0; i < cols.Length; i++)
        {
            switch (i % 4)
            {
                case 0:
                    cols[i] = new float4(0, 1, 0, 1);
                    break;
                case 1:
                    cols[i] = new float4(1, 0, 0, 1);
                    break;
                case 2:
                    cols[i] = new float4(1, 1, 0, 1);
                    break;
                default:
                    cols[i] = new float4(0, 0, 1, 1);
                    break;
            }
        }
        buffer.SetData(cols);
        Material.SetConstantBuffer("UnityInstancing_Props", buffer, 0, matrices.Length * sizeof(float4));
    }

    void OnDestroy()
    {
        buffer.Release();
    }

    // Update is called once per frame
    void Update()
    {
        for (int i = 0; i < matrices.Length; i++)
        {
            matrices[i].m13 += Time.deltaTime * i * 0.1f;
        }
        Graphics.DrawMeshInstanced(Mesh, 0, Material, matrices, matrices.Length, null, ShadowCastingMode.Off, false, 0, mainCamera, LightProbeUsage.Off, null);
    }
}

UnlitConstantBuffer.shader

// Upgrade NOTE: upgraded instancing buffer 'Props' to new syntax.

Shader "Unlit/ConstantUnlit"
{
    Properties
    {
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float4 col : COLOR0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 col : COLOR0;
                float4 vertex : SV_POSITION;
            };
            #if defined(UNITY_INSTANCING_ENABLED)
                #if defined(SHADER_API_GLES3)
                    cbuffer UnityInstancing_Props{
                #else
                    CBUFFER_START(UnityInstancing_Props)
                #endif
                struct {
                    float4 _Color;
                } PropsArray[UNITY_INSTANCED_ARRAY_SIZE];
                #if defined(SHADER_API_GLES3)
                    }
                #else
                    CBUFFER_END
                #endif
            #endif


            v2f vert (appdata v)
            {
                UNITY_SETUP_INSTANCE_ID(v);
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                #if defined(UNITY_INSTANCING_ENABLED)
                #if defined(SHADER_API_GLES3)
                o.col = float4(1, 0, 0, 1);
                #else
                o.col = PropsArray[unity_InstanceID]._Color;
                #endif
                #else
                o.col = float4(1, 1, 1, 1);
                #endif
                return o;
            }

            float4 frag (v2f i) : SV_Target
            {
                return i.col;
            }
            ENDCG
        }
    }
}