I braved the creation of a tutorial to illustrate fading between layers and have discovered that each browser is different in how it handles the layers background colors with C2 r175.
You can test the project here and check the capx from my tut.
Here are the noted browser differences regarding background colors and transparency properties of C2 layers between browsers:
Firefox -- does not recognize the 'Transparent' property of layers cleanly. If 'Transparent' is No, the layer will still be transparent (except for areas around textbox objects) -- and if Transparency is 'Yes' when both a text box (on the transparent layer) and white (or black) background from separate layer is present the shades of white or black in the text box are slightly different -- not cleanly transparent.
Chrome -- perhaps the best -- seems to render as expected.
IE -- Opacity does not persist. Once the opacity of the layer being faded in reaches 100% it goes black. (EDIT - this was sort of fixed in IE by adding a wait 0 seconds to the end of the fade actions -- this prevented assigning the new layer variable too quickly in IE (but added a 'flash' at the end of the fade in IE), and it seems this should not have been necessary due to the order of my events.)
I'm not entirely sure how to address these differences -- file a bug report maybe? ... any suggestions are welcome... and also let this be a good reminder to cross-browser test your projects!