Yes, QT allows any color, but it's a function of the program you're using to generate the MOV ... in other words, you have to render MOVs that way, rather than change them in QT. I'm not sure if Motion allows it, but I'm sure someone else will chime in with that info. In the meantime, I thought it might also be helpful to know that some software or versions of software that you might be bringing your animations into may not recognize or interpret correctly an alpha channel that's represented by anything other than true black ... most nowadays will, but some won't so don't do a 12-hour render on grey until you've tested with the other applications in your workflow.
When i render my animation (which is black) in plays just fine and i can use it just fine in After Effects and Motion but when I want to preview it before i drag it into my project it isn't visable in quicktime due to the fact that the quicktime player is also black... so i cant see the image to preview it.. i wanna change the quicktime canvas BG color to Grey or White.
Not sure I understand your point ... the background is black because you rendered it with a black background ... for example, in AE, if you change the comp's background color to grey and render, it will be grey when you open it in QT.
I don't think you're understanding what I'm saying ... QuickTime, nor any other media player I know of, displays alpha channels as "transparent" and QT doesn't choose to display alpha channels as black ... it displays alpha channels whatever color the user tells it to, which defaults to black in most media generation software. Again, if video is rendered with a grey background to represent its alpha channel, QT will display it as grey .... unless of course the software it's rendered from doesn't allow rendering with alpha channels represented by any color other than black and forces alpha channels to always display black. As I mentioned, After Effects will represent an alpha channel with any color the user chooses ... I don't know that Motion will as I haven't tried it. That's all the help I can offer. Good luck.