Apply effects to layers below

I have a quick webGL effect question.

Say that I want to occasionally apply a webGL effect to everything in the layout, except one object. For example, I want to make everything greyscale except perhaps the HUD, or the player. I also want to have positional control over this effect using a masking object.

If the game has one main layer, I can just use the masking object as expected. Easy. However, if I have multiple parallax / background layers, this becomes very problematic as I now need a large amount of masking objects, all using complex maths to stay with the correct parallax.

Is there any way to make a webGL effect masking object apply its effect 'downwards' to all the layers beneath it? If not, I feel like this would be a great asset to have for the reasons above.

Thanks for your help!

-Sqiddster

can apply the effect to the design you want and separates design that does not have the effect (y)

Aro Guerra, I am not sure what you mean!

This can serve dropbox.com/s/fwk4ntd5b9l7jas/Platform_tutorial-I.capx

Aro Guerra I still don't know what you mean here. All I see in that capx is a regular platform game with a wave effect on the background.