Green

What do you think of when you think of the color green? Money? Sure. Jealousy? Sure. But if you ask our speaker, he'd say one thing and one thing only: youth. And no matter what Kermit says, for this guy, it is easy being green. But as the poem progresses through time, the significance of green changes, too

• Line 2: In a simile, the speaker says he was "happy as the grass was green." He's pretty straightforward about how he feels here, and green seems to embody that feeling. We mean, grass is really green. So this guy must be really happy. 
• Line 10: The speaker says "I was green and carefree"—a slight twist on line 2. In line 2, the speaker is using a simile to compare his happiness to the color of the grass. But in line 9, the speaker says "I was green." Of course, he doesn't mean he was physically green, but he's referencing his emotional and mental state: happy, carefree, young. 
• Line 15: Later in the same stanza he repeats that he was green. He probably means the same thing as he did in line 9, but he's using repetition to build momentum and place an emphasis on that very same feeling. 
• Line 22: The speaker says "fire green as grass." It's possible for flames to be green, at least partially, but more likely, the speaker is using green as a symbol for the happiness and carefree attitude of youth. As he repeats the color, it begins to embody the speaker's emotional state, so whatever he describes as green is infused with the speaker's happiness. Here, he specifically uses a simile to link fire and grass. So even though green is happiness for the speaker, there's also the possibility that the speaker is alluding to the fragile nature of his happiness. Fire would burn up grass, right? He wouldn't have realized it when he was young, but now, looking back and speaking in past tense, he could see the "grass" of his youth was going to vanish. 
• Lines 44-45: Green has changed a bit. Here, the children are "green and golden," but they're being led "out of grace" by time. So, rather than happiness, it seems like green has started to become associated with loss. The children could also be seen as naïve, rather than happy, as if the carefree attitude of youth is being shown in a different light. 
• Line 53: Finally, green has changed completely. The speaker says "Time held me green and dying." He's definitely not happy here, is he? At the beginning of the poem, the speaker was happy and carefree, but as we get to the last stanza, he's realized that time is fleeting, and so is his happiness. Green has changed from a color of vitality to a color associated with death. Just like the speaker uses words that can have multiple meanings, he's used green as a symbol for the various emotions he feels about being young once.