Colliders don't work on another collider

We are making a Hot-Cold game, where you need to select an object with a crosshair that answers a level question. We have three colors for fire: red is the correct answer, yellow is the answer is near, blue is the answer is far. We are trying to do this through several polygon colliders using tags,
but they do not work adequately (another collider often responds). Please help with the solution of this issue.

Script:


public class PoligonButton : MonoBehaviour
{
public void OnMouseDown()
{
switch (this.tag)
{
case "MainTag": // This tag stay on elephant
Debug.Log("on");
break;
case "NearTag": // This tag stay near elephant
Debug.Log("near");
break;
default: // If far from the answer, untagged
Debug.Log("off");
break;
}
}
}

 

We have two objects with colliders, they are on top of each other. We need to handle clicks on these objects.
Blue is above the red object and when you click on it, both objects are clicked.
We want only blue to be clicked when blue is clicked. And when you clicked on red, only red was pressed, excluding the place,
where the blue object lies.

 

The crux of the problem is that the collider lies on the collider. When you click, sometimes on the same point, both colliders can respond, they begin to get confused.
More or less, the installation of a rigitbody on these objects saves the situation, but all the same, there are small places on the objects where a different collider can respond at the same point.
And when setting the permission, something stops working when the game starts.
We need to understand why two colliders, when they are on top of each other, start to conflict. And with and without rigitbody.
We cannot use buttons and anything else, since our objects are not square, but polygonal, and we need just such a pressure range.
We tried to find the pressed point in the following way:

void Update ()
{
if (Input.GetMouseButtonDown (0))
{
Vector3 mousePos = Camera.main.ScreenToWorldPoint (Input.
mousePosition);
Vector2 mousePos2D = new Vector2 (mousePos.x, mousePos.y);

RaycastHit2D hit = Physics2D.Raycast (mousePos2D, Vector2.zero);
if (hit.collider! = null)
{
Debug.Log (hit.collider.gameObject.name);
}
}
}

And so, too, colliders start to get confused,
even worse than the previous way.

Maybe I'm not clear explaining the essence of the problem. If so, sorry, I'm Russian.

 

Okay, moving along Z helped us so that all colliders are at different distances. This is the only thing that worked.