How to set the alpha component of an annotation?

Q: One question regarding setting a color on our Square. The Square (which should actually be called Rectangle) has set*Color methods. The paramter ColorPt class takes x,y,z,w params (which should be called r,g,b). What i am struggling with is setting the alpha of the color. the w parameter does not seams to be alpha. How would i set the alpha component of my Squares color, or how could i turn the square semi transparent?

However, you could use the Markup class setOpacity method.
Markup m = new Markup(annot);
A: No, the ColorPt class does not take into account of opacity. The three params constructor is for RGB and the four params constructor is for CMYK.