This was a problem with the way that MACs handle the Unity Fog, the following code allowed me to fix it. I added a script to my GUICamera and no more fog in the way of my ui :D

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    private bool revertFogState = false;
    void OnPreRender() {
        revertFogState = RenderSettings.fog;
        RenderSettings.fog = enabled;
    }
    void OnPostRender() {
        RenderSettings.fog = revertFogState;
    }
}

http://unity3d.com/support/documentation/ScriptReference/Camera.OnPreRender.html