^I presume you're using the "Tween" function?
Basically you need to make sure your ending frame layer is also visible in the first frame.
So for example if you want to fade an image to white..
If you have the starting frame like this:
(Picture layer visible, white layer invisible)
And the ending frame like this:
(Picture layer invisible, white layer visible)
If you then tween those frames, what will happen is:
- the picture layer will tween from being 100% visible to 0% visible
- the white layer will tween from being 0% visible to 100% visible
This means that in the middle frames, both layers will be semi-transparent
What you want to do instead is have the starting frame like this:
(Both picture layer and white layer visible)
And the ending frame as before:
(Picture layer invisible, white layer visible)
Now what happens when you tween the frames:
- the picture layer will tween from being 100% visible to 0% visible
- the white layer will not change, and will remain 100% visible in all frames