A grey area is a topic with no clear solution, often because there are no known rules or because it is hard to decide what is right or wrong.
When it comes to the law there are many grey areas.
The difference between flirting and harassment is a grey area.
Another related expression is shades of grey. It is also used when it is not clear what is right or wrong.
Many children's stories say the world is full of black and white choices. In reality there are many shades of grey.
The Empire State Building opened during the Great Depression in 1931 and was the tallest in the world until 1972 when the World Trade Center was finished. The structure is perhaps best known for being climbed by a huge ape in the 1933 movie version of "King Kong".