If you read a couple pages of the story after Ponyboy recites it, he and Johnny give a good interpretation. Or rather Susan Hinton describes it well.
Nature's first green is gold
Her hardest hue to...
In Neglect
THEY leave us so to the way we took,
As two in whom they were proved mistaken,
That we sit sometimes in the wayside nook,
With mischievous, vagrant, seraphic...