Can colour be an idea?

A shopping receipt may seem like a strange thing to put on an art gallery wall. How can this be art? Rather than making a painting or sculpture, there are many artists (like Ceal Floyer here) who create art from everyday things. She would like you to think about the idea behind the art, rather than what it looks like. Take a closer look at the receipt. You will see that it is a list of objects bought from the supermarket that are all white. Imagine the objects and their whiteness and think about why this might be in a display about colour. Is white a colour?