I'm about to start making MMF for a cake for this weekend -- and I bought a "professional strength" red gel color, and a powdered red color. Anyone know which might be best? And if it's the powder - any idea how much to maybe start with for red?

Also - I know colors tend to darken when they dry - is it the same for MMF if I add the color to the MM's before I add the sugar? Or will it lighten on me after I add the sugar.

The gel color is probably better than the powder, since it will dissolve completely. You can add it to the melted marshmallows, and it will take a LOT of color. The sugar will cause it to lighten, and time will allow it to darken.