How 2 have certain color in layer below make parts of layer above transparent

Question

I have an opaque layer. The underlaying layer has green spots. I want those green spots to "shine through" the upper layer. How? In Photoshop there are blending modes, I haven't found anything similar in AE. I use AE CS5.

Answer 1

The blend modes in AE are just like the blending modes in Photoshop. I think you're looking for the Blend If layer style.
Or you might be looking for this:
The first can be brought into After Effects by importing a PSD as a composition with the Blending Options set in layer styles. It will show up under Layer Styles and can be copied and pasted to other layers. Unfortunately, you cannot make the blend adjustments in AE, you can only turn the effect on or off. The API's just don't exist that allow that to happen.
It looks like this in AE:
The second, Preserve underlying transparency is just a check box in the timeline. I use this feature all the time. You'll find the box between the blending modes and the track matte. There's a T at the head of the column. In a strange twist, this feature does not come into the timeline when you import a PSD as a composition, it must be turned on manually.
Hope this helps. I actually use both all the time.