Suppose you have let LaTeX draw several rules in different colors on top of each other without transparency, so that you only see the last rule drawn in the pdf file. What does this mean for printing the pdf file? Will only be printed what you see, i.e. the topmost rule? Will all lines be printed on top of each other?

How do you strictly distinguish not wanting a color, so that the color of the medium to be printed is the result, from wanting a document background color?

How do you specify that a certain background color must be included when calculating transparency effects, but that this color does not need to be printed because it is the color of the medium to be printed?

(This refers to xcolor and tikz)