adding annot rect with different transpiracies

Hello,
I'm trying to use
page.AddAnnotRect(rect, vpage.ToPDFSize(3),x,y );
with x and y having different color transpiracy (x = A1A1xxxxxx ) and (y = A2A2yyyyyy) with A1A1 diferent from A2A2. But what I get as a result is an annot only one level of tranpirancy in both of the colors. How can I correct that?

That's standard from PDF1.7 standard manual.
No way to avoid that behavior.