How do we know that poet leaves the cornfield before the Skylark has stopped singing??

We learn the poet is the first to leave the field in the last two lines of the poem.

From the text:

And as I paused to hear his song
While swift the sunny moments slid,
Perhaps his mate sat listening long,
And listened longer than I did.

The poet has used many colors in the poem. List the colors. What according to you does each color symbolise