They are both great games, but i'd say sonic colors
Sonic Colors
No, it is the direct sequel to Sonic the Hedgehog 3 released in 1993.
This should be in sonic unleashed.
There will be 2 options: Play as the original Sonic in the original levels, or play as the newer Sonic in levels like in Sonic Colors or Sonic Unleashed.
Sonic Unleashed is 7+
Sonic Unleashed happened in 360.
unleashed
yes
Sonic will transform into a werehog during the night in sonic unleashed.
Depends on your choice. At sonic unleashed WII/PS2 version is sonic colours surely better. At sonic unleashed XBOX360/PS3 version it depends on what you like, the most will like sonic colours more where it's more based on speed. At sonic unleashed you have a lot of werehog stages which are slowly and in my opinion very good, but doesn't fit in a sonic game. This is just an opinion of me, maybe you think different about it so to find that out you can watch some gameplay movies on youtube. ;)
Sonic and the black knight that game is so much cooler than Sonic Unleashed. I mean is Knuckles in Sonic Unleashed? No. Is Shadow in Sonic Unleashed?No. Plus there playable too on Sonic and the black knight.And is Sonic Unleashed multiplayer?.N-O. But Sonic and the black Knight.
Yes, there are Sonic games after Sonic Unleashed. At the time of writing, the latest will be Sonic Generations.