the reporters admire him.  Pony also admires him, because he can’t feel comfortable in his own skin.

I swear, sometimes he reminds me of a colt.

The above quote comes from chapter 7. The chapter starts off in the hospital, because Johnny and Dally are there in order to get their injuries from the fire taken care of. Reporters are all over the place trying to get the scoop on the story of a Greaser gang rescuing children from a burning church. Soda is loving every minute of the attention. He's showing off to the reporters and really strutting about in an attempt to soak up all of the limelight.

Ponyboy compares Soda to a colt, which is a young horse. Pony believes that a colt does the same thing as Soda is doing. They both try to get all of the attention that they can.

A long-legged palomino colt that has to get his nose into everything. The reporters stared at him admiringly.

Keep in mind that Soda is movie star handsome. Add that to his infectious energy, and people can't take their eyes off of him. That's what a young, beautiful horse does to people. You can't take your eyes off of such a pretty, majestic, and energetic animal.

A colt is a young male horse, known for being full of energy, always wanting to move, and having a "gangly" body.  Gangly means tall, thin and awkward.  A colt is awkward because, like a puppy who has to grow into his paws, a colt has not yet grown into his legs.  They are often too big for his body, and so it seems when a colt moves that his limbs are going everywhere.  Ponyboy thinks of Sodapop like this.  Always moving, limbs going everywhere, tall, thin, and not quite in control of himself because of all the energy he has.  Although Ponyboy doesn't really understand at first, this is part of why Soda doesn't do well at school.  He can't sit still.

This comparison coincides with Ponyboy's recollection of Mickey Mouse, the horse that Soda used to ride.  Ponyboy tells Cherry Valance how Mickey Mouse and Sodapop were alike, both "ornery", meaning both stubborn and full of life.

Ponyboy's description of Sodapop as a colt is significant for several reasons.  The first is physical.  Sodapop is lean and wiry, like a colt would be.  Such physicality quickly pivots to an emotional aspect.  In chapter 7, Sodapop is intrigued with the media attention.  He shows this through vigor and a sense of excitement.  Like a colt, he wants to know what is happening and desires to be the center of attention.  This description underscores his characterization.  Throughout the narrative, Sodapop is true to his name as "bubbly."  He is "always happy-go-lucky and grinning."  Sodapop is also described as one who "gets drunk on just plain living." These reflect a person who is more entranced with the moment.  Sodapop wishes to be immersed in the direct action of life, of being in the world.  Sodapop is not someone who is overcome with melancholy, or resigns himself to distant reflection.  He is of the moment.  Like a colt, he wants to be involved with everything and wants to be immersed with the instant.  

Sodapop being a colt is a reflection of his active nature.  He is engaged, locked into this instant.  He desires to be a part of it.  Ponyboy's description of him holds significance because it is almost an exact opposite description of Darry and Ponyboy.  Sodapop is so intrigued with everything around him, as a young colt would be.  Darry has come to see the bitterness that life can offer and thus is a bit more distrustful, while Ponyboy is reflective of the nature of being in the world.  Both of these contrast with the young, excitable, and "coltish" nature that Sodapop displays.  Ponyboy's description is reflective of this condition of being in the world.