Do you have to go back to Black to get Cyan?
Black and Cyan is only the firmware, not the OS. No matter how many developer preview releases you've installed, you always had Black, so there is on way to "go back" to it... you are still on it.
Either way though, the answer is "no".
When Nokia releases Cyan, they bundle it with the OS, and your device will prompt you to download it. You will effectively receive both, but the OS bits will be 100% identical to what is already on your device at that time (assuming you still regularly download developer preview updates,
like the one that was released today)
I think all of your questions are also answered in this thread:
http://forums.windowscentral.com/win...questions.html
Hope that clears things up.