This is a 4 year thread that is talking about the first generation Apple TV and its white remote. It no longer applies today.
For newer Apple TVs, any silver remote will work without pairing to control any newer Apple TV including the 4th generation Apple TV.
If you have a 4th Generation Apple TV and want to pair a new black siri remote to it:
1. Place the Siri Remote within 3 inches (about 75 mm) from the Apple TV and point it at the Apple TV.
2. Hold down the MENU and VOLUME UP buttons for 5 seconds. Note that these buttons are placed diagonally from each other, so you might need two hands.
After a few moments a message stating the remote is connected should appear on screen.