pic2
http://www.cplotts.com/2009/06/16/blend-modes-part-i/
http://www.cplotts.com/2009/06/16/blend-modes-part-ii/
http://www.cplotts.com/2009/06/17/blend-modes-for-silverlight/
http://www.cplotts.com/2009/06/30/blend-modes-part-iii/
http://www.cplotts.com/2009/11/06/blend-modes-now-opacity-aware/
http://www.cplotts.com/2009/11/29/blend-modes-hue-saturation-color-and-luminosity-with-wpf-4-0/
I am not sure how to achieve multiplicative blend mode using this, but it might be worth looking into.
We will be looking into it at some point in the future, but I am not sure when. So if you are interested in attempting it yurself, you could take a look at the above blog posts.
Best Regards,
Tomas Hofmann