Create a macro that does the FILE->PRINT (call the macro PRINT). The create a button (you can use a create square from the drawing toolbar). Place some text in it, say "PRINT".
Then click on SLIDESHOW and ACTION SETTINGS. Click on the RUN MACRO radio button, and select the PRINT macro you recorded earlier. At the bottom, click on HIGHLIGHT CLICK (which will confirm that you have clicked the button).
Click OK. Now everytime you run the slideshow, and click on the button, it should not only change colour, but also print to the person running the slideshow's default printer.