Someone told me that I could dye my marshmallow fondant while making it... Has anyone tried this? I need to make a pretty dark blue and was thinking of putting some color in while making it. What are your thoughts?

If I need alot of one color, then I always dye it when I am making it. I start to add the dye when I am mixing in the icing sugar
If I only need a bit then I just mix the color in later.

You certainly can! Just add the color to your melted marshmallows before adding the powdered sugar. It is SO much easier than trying to add the color once you have made it, especially for darker colors.

Thanks! Now will it lighten up when I add the sugar? Or should I make it the color that I want it to be?

Yes it will be slightly lighter, but really not that much. Plus, the overall shade will darken if you let it sit for a few hours, so it will be pretty close. Give it a try - it really is a huge timesaver!