Green Side Up

A painting contractor was speaking with a woman about her job.
In the first room she said she would like a pale blue.
The contractor wrote this down and went to the window, opened it, and yelled out :
- Green side up !
In the second room she told the painter she would like it painted in a soft yellow.
He wrote this on his pad, walked to the window, opened it, and yelled: - Green side up !
The lady was somewhat curious but she said nothing.
In the third room she said she would like it painted a warm rose color.
The painter wrote this down, walked to the window, opened it and yelled :
- Green side up !
The lady then asked him :
- Why do you keep yelling "green side up" ?
- I'm sorry, came the reply. But I have a crew of blondes laying sod across the street.