All right, so remember how Draco disarmed Dumbledore at the end of the sixth book? That means that Draco would be the master, but then Harry disarmed Draco later. Even though it wasn't the Elder Wand Draco had, Harry became the master because of that. That's how most interpert it anyway.
Harry defeats Draco Malfoy who had disarmed Dumbledore. That made him the owner of the Elder Wand and when Voldemort tried to use it against Harry, it wouldn't kill it's true owner.
i think it was all planned out by dumbledore!
Actually when Draco dis-armed Dumbledore in The half Blood Prince, at the end right before Dumbledore was killed, the elder wand would then work for Draco, Then in the Deathly hallows when Harry dis-armed Draco that allowed him to be able to use the elder wand but he doesn't get the chance to use it until the end of the Deathly Hallows. Voldemort takes the wand off Dumbledore but that isn't enough to make it work for him because Harry is truly the owner. So when voldemort tries to kill Harry it wont kill him because he is the owner so it rebounds on voldemort therefore killing him!
because harrys wand and 'voldemorts' are twins so the can 'wound but not fatally harm one another'
There's no symbols on the Elder Wand. (Perhaps in the film, but the films have nothing to do with the book.)
The elder wand is passed down when the original owner is disarmed or is killed. The person who disarmed\killed the owner is now the owner of the elder wand.
Actually, Dumbledore didn't intend on Harry getting the Elder Wand. As said in "Harry Potter and the Deathly Hallows", the only way you become the master of the wand is either you disarm the master and/or, you kill them. So when Draco disarmed Dumbledore in the sixth book that made Draco the master. In the seventh book, at Malfoy Manor, Harry disarmed Draco by taking his wand, making him the master of the Elder Wand.
The wood of the Elder is hard and heavy. It is white in color and has a fine close grain. With this in mind, you would expect the Elder Wand to be white in color - although with age it might begin to darken a bit to a grey or brownish color.