Shadow's emerald: Red.

After the other six emeralds are retrieved, it's up to Shadow to find the last one to save his arch rival, to this theme. www.youtube.com/watch?v=c0zvUw… Like Omega's one, it's action packed, but it has a haunting tone to it. This could be because it's the final chaos emerald to find, but... it's also because he secretly misses Sonic and wants to help him get better. The emerald is red, which shows their rivalry, but also that Shadow will aid Sonic when called for... like now.

Also, little love triangle hint between Rouge/Shadow/Amy. I ship Rouge and Shadow, but Amy and Shadow I find kinda cute as well.