I asked this question last November as it something myself and a lot of other users are finding frustrating at the moment. Its a known bug which appears to be a difficult one to fix (given the time its taking).
To quote Lars on the issue:
'(Transparency is currently not working in live mode I'm afraid, we're working on that!)' (1).
Currently I don't know of any work around's to resolve the issue but rest assured that I keep reminding the Capture chaps about the problem. I do hope we get it fixed soon as not being able to visualise a gauze is a real limitation of Capture at the moment.
(1) -
http://www.capturesweden....e/posts/Default.aspxCheers
Mike.