A blue house has blue bricks; a yellow house has a yellow bricks. What is a green house made of?

“Green bricks”

The riddle plays on the double meaning of 'green house' as a structure made of glass for plants, rather than the color of the bricks, which misleads to think it should be made of green materials.

“Green paint”

While a house can be painted green, the riddle specifically refers to a 'green house,' which is a type of building made primarily of glass for horticultural purposes, not simply its color.

“Plants”

Though a greenhouse is used to grow plants, the riddle is asking about the material of the structure itself, which is glass, not the contents or purpose of the house.