You can have LaTeX draw frames around things that are placed inside boxes.
\fbox for this.
How can you have LaTeX draw lines, e.g., frames around things, which are visible when viewing the resulting pdf-file on screen but which do not get printed on paper?
This would be nice in the process of creating printable labels where in the pdf-file you would like on the screen to see squares denoting the borders of single labels while there is no need to have these squares/borders printed.
More general: How can you have LaTeX place things into the pdf-file which are visible when viewing the resulting pdf-file on screen but which are invisible when the resulting pdf-file is printed on paper/which do not get printed on paper?
Can you have color specifications for colors which are shown on screen but not printed on paper?