MATH PUZZLE: Can you replace...

A painting contractor was speaking with a woman about a 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."