Its driving us crazy not knowing! what is this bird?

I am in Kansas, we live in the country with a hay meadow on one side and dense woods on the other, a 1/4 mile from a river. Me and my sister know the birds around here by site and sound and when we see a new one we look it up.
The other day my sister saw a bird that she thinks was built more or less like a tanager as far as size/size and shape of beak, it’s back was gray with a tint of green the belly was a bright neon yellow and it had a bright neon red collar / ring around its neck. It was perched in a tree at the edge of the woods looking out towards the meadow singing away. Have only seen it once.
We have gone through our bird books with a fine tooth comb and searched the Internet. I am thinking he isn’t native to north America or something?
Help?!!!
Thank you for your thoughts and suggestions.
those are not the bird we saw, thanks!

Saffron Crowned Tanager: http://www.naturetrek.co.uk/pics/mp_Saffron_crowned_Tanager.jpg ??

That’s all I got. o_O They aren’t US birds.

Or maybe Western Tanager: http://sdakotabirds.com/species/photos/western_tanager.jpg

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