Question

The first answer is the basic correct answer, but there are variants.

1. Don't change the background colour (waste of ink), rather use pgfpages to put a border around each frame (this isn't one of the standard page-type declarations, but it isn't hard and I can make mine available if anyone wants it).

2. It's possible to change the type of the output (between beamer, handout, trans, or article) without modifying the file. The trick is to put the main document in one file, say geometry.tex but without the documentclass declaration. Then you create a new file for each type with just the documentclass declaration. For example, geometry.beamer.tex could contain:

   \documentclass[12pt,t,xcolor=dvipsnames,ignorenonframetext]{beamer}
   \input{geometry.tex}
   

   whilst geometry.handout.tex might contain

   \documentclass[12pt,xcolor=dvipsname,ignorenonframetext,handout,%
    notes=only%
   ]{beamer}
   \input{geometry.tex}
   

   and geometry.article.tex might be

   \documentclass[a4paper,10pt]{article}
   \usepackage[envcountsect]{beamerarticle}
   \setjobnamebeamerversion{geometry.beamer}
   \input{geometry.tex}
   

   Not only does this make sure that you are always compiling the correct version of the document, it also means that if you use a version control system then it doesn't keep complaining about you modifying the file just because you change the output type.

3. If you are strong in the ways of beamer and TeX, you can go one step further. I use beamer for lectures which means that one single file contains the beamer versions and the handout versions of nearly 30 lectures. To produce a given version of a given lecture, I need to have a way of telling TeX what I want. I could have 60 separate files all with variations on the above, but I've found a simpler way is to have TeX examine the jobname to determine this. Then I just have to have 60 symlinks to the main file (and I can create all 60 symlinks with a single zsh command). That is, lecture.beamer.2009-11-19.tex is a symlink to lectures.tex and when I run LaTeX on it then I get tomorrow's lecture in beamer format (well, I would if I'd written it yet). Again, I'd be happy to share the code for this if anyone's interested.

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Addendum 2012-11-13 Unsurprisingly, an early question on TeX-SX was essentially exactly this one. Also unsurprisingly, I answered there as well and as that place is more suited to TeX answers than this one I incorporated this answer there. That answer can be found at http://tex.stackexchange.com/a/1426/86 which also contains links to my code for the above.