Give your sweetheart a message as key chain. Use the Customizer to change the text as you like. This thing is multicolor by only changing the filament during printing, no dual extrusion is necessary. Please read the instructions. Of cause you can also print it monochrome. See also my Customizable Heart Shaped Magnetic Buttons "Words from the Heart"Layer height: 0.25 Infill: 100% !!! I used Cura with the standard "Pause at Height" Plugin. So color change is really easy and exact, at least on Prusa i3 and similar printers. For the settings I have used, please refer the screenshot in the gallery. The printer pauses on the correct layer for color change. After changing the color you have to press a button on the printer. Another methode is shown by EtienneDusablon here.