Its strange why they didn't grow white, red, pink cosmos (I learned that its slightly different - Cosmos bipinnatus).

Most of Korean has bright memories with this flowers which is almost symbolic to crisp days in Autumn.  
For me, it has another meaning.  

I flunked a few classes in the University and have to stay another one more semester.  

Koreans calls the one semester delayed graduates "Cosmos Graduation" for they released in Autumn, with the background with this lovely flowers.

September 1999

I got some details about cosmos from Virtual Garden;

Few plants grow as rapidly as cosmos, and fewer still have such graceful flowers. 

These natives of Mexico become 4 to 6 feet tall, sometimes taller, and bear airy, daisy-like blossoms 2 to 4 inches across.

The wide, serrated petals circling yellow centers may be pink, red or white. 

The foliage is delicate and feathery. 

The species known as yellow cosmos, which seldom grows more than 3 feet tall, used to begin flowering so late in the season that fall frosts often nipped the first blossoms. But now there are early flowering yellow, orange and red varieties.