This is a Unity3D script that works around colliders intercepting mouse messages when they should not. By using layer mask, this script sends messages to only those objects that need it.

MouseEventSender

using UnityEngine;

public class MouseEventSender : MonoBehaviour
{
    public float RayCastDistance = float.MaxValue;
    public LayerMask LayerMask;
    public Camera Camera;
    public int Button;

    private Collider m_LastHit;
    private Collider m_PressedOn;

    public void Update()
    {
        var cam = Camera ? Camera : Camera.main;
        var ray = cam.ScreenPointToRay(Input.mousePosition);

        Collider hit = null;
        RaycastHit hitInfo;
        if (Physics.Raycast(ray, out hitInfo, RayCastDistance, LayerMask))
            hit = hitInfo.collider;

        if (hit != m_LastHit)
        {
            if (m_LastHit)
                m_LastHit.SendMessage("MouseExited",SendMessageOptions.DontRequireReceiver);
            if (hit)
                hit.SendMessage("MouseEntered", SendMessageOptions.DontRequireReceiver);
        }

        if (hit)
        {
            if (Input.GetMouseButtonDown(Button))
            {
                hit.SendMessage("MousePressed", SendMessageOptions.DontRequireReceiver);
                m_PressedOn = hit;
            }
            else if (Input.GetMouseButtonUp(Button))
            {
                hit.SendMessage("MouseReleased", SendMessageOptions.DontRequireReceiver);
                if (hit == m_PressedOn)
                    hit.SendMessage("MouseReleasedAsButton", SendMessageOptions.DontRequireReceiver);
            }
            else if (hit == m_LastHit)
            {
                hit.SendMessage(Input.GetMouseButton(Button) ? "MousePressedOver" : "MouseOver", SendMessageOptions.DontRequireReceiver);
            }
        }

        m_LastHit = hit;
    }
}