Multiply blending mode

Hi all,

I need to do multiply-blending in my application:
I have several components stacked on top of each other, and the last one is a paint layer, whose alpha-channel has to be overlaid with a colour and then multiplied by the pixels of the layers below (the painted parts of the layers below are grayscale-only).

What would be the best and more efficient way to do that kind of thing using Juce ?

Thanks for your input.