iPhone webview - chroma keying possible? (how can I make a color transparent)

I have an iPhone app that has to show web content on top of it.(an webview on top) Normally I would make the webview transparent and then I simply see what is beneath. That is ok, but not entirely.

开发者_如何学PythonI would like to be able to set a Chroma Key = a color that the webview will make transparent so that I see my app beneath.

Is this even possible in iPhone webviews? Thanks, Neal