PlayerColor.cs

using UnityEngine;
using UnityEngine.Networking;

public class PlayerColor : NetworkBehaviour
{
    [SyncVar]
    public Color color = Color.white;

    private void Update()
    {
        GetComponent<SpriteRenderer>().color = color;

        if (isLocalPlayer && Input.GetButtonDown("Fire1"))
            PickRandomColor();
    }

    private void PickRandomColor()
    {
        var newcolor = new Color(UnityEngine.Random.Range(0f, 1f), UnityEngine.Random.Range(0f, 1f), UnityEngine.Random.Range(0f, 1f), 1f);
        CmdSetColorOnServer(newcolor);
    }

    [Command]
    public void CmdSetColorOnServer(Color newColor)
    {
        color = newColor;
    }
}