How did you capture them? Did you mean to say that you imported them? Import and capture are two completely different things. Importing uses and doesn't change the original file. Capturing creates new media which may or may not be based on the same settings as the original file.
If you imported them, I'd say your problem is that you're trying to use AVI files. FCP doesn't really like them. Your best bet is to convert them into another format using Quicktime or some other conversion program (maybe Compressor will do it too).
However, sometimes there will be a color/luminance shift. That happened to me once. In that case, the files had to be converted to quicktime on a PC instead of a mac. Not sure why but it fixed the problem.
Andy