Doing scratch and sniff is fun (and easy!) I use 1:1 embossing powder and sugar-free Jello. Green eyes is right in saying to use only _sugar free_, but mainly because the sugar carmelizes and makes a sticky mess.
I've found that you do need some color behind the embossing mixture, but since I don't have any craft pads, I stamp using my classic pads, then stamp the Versamark over it and emboss that. Here's a sample of one I did recently:
Gallery at Splitcoaststampers
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Happiness is being kneaded.
Avatar is my childhood kitty, Berries.