can you answer this riddle?

[Noora]

when you buy me i am green
at home i am red
what am i?

 

[Doll face]

Watermelon

 

[grub]

an alien prostitute

 

[BLT]

Ripened tomato. Or a person with changing perspective on global warming.

 

[Flare06]

A really slow traffic light?