The Yellow in this spiritual portrait represents Robb's dominant trait, his realistic outlook. In Introverts, the dominant trait is directed inwardly, and spiritual portraits use a long horizontal line to represent this. He demonstrates this trait when he sacrifices 2,000 men in a feint so that his larger force could acheive an easy victory elsewhere.
The Green in this spiritual portrait represents Robb's auxiliary trait, his preference for making logical rather than emotional decisions. In Introverts, the auxiliary trait is directed outwardly, and spiritual portraits use a vertical line to represent this, because it is more evident than the dominant function. He demonstrates this trait by winning many battles early on in the war for the throne.
King in The North
I thought Robb Stark's spiritual would be more colorful — more like his father Ned's or his half brother Jon's portrait. So I was surprised to see the result looks more like Jaime Lannister's than those of his close relatives.
This may be because we do not get to see all that much of Robb. Indeed, most of what we see of him is in his role as commander of the North's military forces.
Tell Lord Tywin, winter is coming for him. Twenty thousand northerners marching south to find out if he really does shit gold.
Over the past few years I have watched the first few seasons of the show several times, and in the month or so just prior to creating this portrait, have seen all episodes featuring Robb and his mom at least three times (including all the commentary tracks). This has inured me to much of the violence in the series in general and in the Red Wedding in particular.
Not only that, repeated viewings makes it easy to see the events from Walder Frey's point of view, and even find humor in some of his snide comments and facial expressions. I'd guess that Walder is another ISTJ; maybe someday I'll find the time and motivation to find out for sure.