This is a still from Danaerys' vision when she was trying to free her dragons in the second season.
The Iron Throne and the throne room in King's Landing.
What's that coating everything?
Snow.
Also, this little tidbit from Melissandre's chapter in
A Dance With Dragons:
What do you see, my lady?" the boy asked, softly.
Skulls, A thousand skulls, and the bastard boy again. Jon Snow. Whenever she was asked what she saw within her fires, Melisandre would answer, "Much and more," but seeing was never as simple as those words suggested. It was an art, and like all arts it demanded mastery, discipline, study. Pain. That too. R'hllor spoke to his chosen ones through blessed fire, in a language of ash and cinder and twisting flame that only a god could truly grasp. Melisandre had practiced her art for years beyond count, and she had paid the price. There was noone, even in her order, who had her skill at seeing the secrets half-revealed and half-concealed within the sacred flames.
Yet now she could not even seem to find her king. I pray for a glimpse of Azor Ahai, and R'hllor shows me only Snow.
All the signs have been pointing towards Danaerys taking the Iron Throne for most of the story. The conquering queen with her dragons and her barbarian horde and her imperious nature and all of that.
Which is exactly why she's not going to.