Who Knows

Riddle: What's taller than a thousand trees growing taller and taller by the season. It's yellow and orange and sometimes it's pink. It has no mind but often thinks. When it falls the world will crumble but not a human mind will be troubled. Laughing and smiling without voice joking and speaking without mouth. Up, up, up, it goes where it stops no man knows. Moving forever without being seen but whispering softly into the green. (the green stands for grass) What is it?