exclude layer from blending in AE

[Joseph Arpaia]

I have a layer with a background image. I have two shapes above that and I want their colors to blend where they overlap. I have the background layer set to blend mode "Normal". The other two layers are set to "Color Dodge". Unfortunately the background layer seems to be blending with the other two layers. I have changed the blend mode of the background layer to every possible option but none of them stop it from interfering.

I can reduce that interference by reducing the opacity of the background layer. My work around has been to darken that background excessively and then reduce the opacity. 

But there should be a way of preventing the background layer from interfering with the blending of the two  shape layers above it. I cannot find instructions for this in the manual page on blending modes. I have seen references to "exluding an layer from blending" in a couple of posts, but no instructions for doing so.

I appreciate any pointers to the instructions for doing this.

Thanks

[Roland Kahlenberg · Accepted solution]

Precompose the two Shape Layers so that youend up with a new composition of these two layers. The resultant nested comp will not Blend into the background layer UNLESS you enable its Collapse Transformation switch.
HTH

[Joseph Arpaia]

Thank you very much.

[Roland Kahlenberg]

You're most welcome.