This is the image for the list view. I copied each state image directly from the Windows 7 theme file. Note that it uses pre-multiplied alpha, so most applications (i.e. Gimp, your web browser) render it darker than it should be.
This is what the grid preview looks like in Skin Studio. As you can see, the image is translucent.
And this is what it looks like in Explorer with the theme applied.
As you can see, it's way lighter than the normal Windows 7 theme.
In case you are wondering if I have any extra settings, this is what the code tab shows:
The use of pre-multiplied alpha is not the problem, as I see the exact same thing when using normal alpha.