indexOf() in an array of movieClips

Hello… I wanna ask something
I have an array of movieClips and I can’t retrieve the elements position with indexOf()


var menuArray:Array =
[
{menu:menu_verde, display:display_verde},
{menu:menu_rojo, display:display_rojo},
{menu:menu_negro, display:display_negro},
{menu:menu_blanco, display:display_blanco},
{menu:menu_azul, display:display_azul},
{menu:menu_amarillo, display:display_amarillo}
];

When I write

trace ("position "+menuArray.indexOf(menu_negro));

I got “position -1”, and -1 is what appears if the element wasn’t found, am I right?
Can you please tell me why is this due to ? Is not possible to find the value with this array’s schema?

Excuse me about my weak english
Thanks. Lio