Photoshop :: Gradients - Algorithm Of Working

9.0 CS2, but it is not so important, because the questions are fundamental.

Gradient Overlay
 
1.  Look at the gradient settings scale. Why gradient isn't  stopped at the second opacity stop and go on till the edge of the settings scale? After all, following the logic it’s the opacity stop and the gradient filling have to be stopped at it. That is to say If the logic of gradient algorithm is next. Filling begins from the left edge of the settings scale and stops at the first opacity stop(this filling is initiated by first markers). Then it continues since first markers and stops at the second opacity stop(this filling is initiated by second markers). But in practice filling continues since second markers also, though there is no third markers which initiate it.
 
2. Why second markers are necessary(they can’t be deleted)? I can suggest if second markers would be deleted and the first would be moved to position of the second,  we would got the same gradient preview. Of course if the filling begins from the left edge and is initiated by the markers as I wrote above.
 
3. User color – you can set fixed color, which you can choose for the future in a dialog window. The window can be called via click to the pointer near the color icon.

When I click the pointer I see only one window where are three text items – foreground, background, user color. All is clear about foreground and background, they are set in two squares in the tools palette.  When I choose “user color” there is no any window is appeared  which have to contains at least current user color icon, color picker window, and buttons that allow to tune and apply user color: “set as user color sample” for picked color, “use user color sample as user color”.  So how I can tune and choose user color?
 
Gradient:
4. I use gradient tool from tools palette. I spent it since canvas top edge till guide line.  What is the gist of spending it for a specific distance? Why the color of first color stop fills the space till the guide line changing  and stops at some light blue. And then monotonically fills with it all distance from guide line till canvas bottom and have no any opacity changes at bottom. Although it have to have some opacity changes because them present in the end of gradient settings scale.