Two Jews are discussing about whether black is a colour or not. They finally decide to go and ask their rabbi about it. Their rabbi plays a long time with his long beard, and then says: “Ya, black must be a colour.”
A few days later, the same Jews are still having a chat, this time to know whether white is a colour or not. So, once again, they go and ask their rabbi about it. The rabbi thinks deeply, and then replies: “Ya, white is a colour too!”
At those words, one of the two Jews declares triumphantly to his fellow: “So, you see, I’ve sold you a color television!”