Hey, me too! I didn't mix in any color as I didn't want to push fate 
...just wanted to try and get the cake covered. I'm definitely interested in the answer to this.
I also found that there was absolutely no give...but I think it might be because there's no glycerin??
If you're only needing it for one color, add the color in with your flavorings and stuff before you melt your marshmallows. If your needing it for several colors, I think it just takes some good old elbow grease and muscles!!!!!
What MMF recipe are you using? Rhondas Ultimate has fantastic texture and taste, and the give is really good too, if you feel you need a little more which sometimes I do I just add about a tsp or 2 of glycerine, it gives it stretchieness and doesn't compromise texture at all. As far as color mix in's if it is a dark color I have noticed it really compromises the give and pliability, I haven't found a solution to that yet.
Truthfully, the MMF will never have the same consistency as commercial fondant no matter what you mix in. I do use MMF sometimes, especially if it's a "freebie" cake to cut down on my costs. However, I've added corn syrup, Crisco, lemon juice (??), glucose, glycerine...all to no avail. The consistency just isn't the same. I do use fondant recipes that work well and have the same consistency as commercial fondants. There are several good ones on this site.
Rhonda's Ultimate is my go to recipe for MMF, otherwise I would use the fondant recipe from the Cake Bible
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