I'm going to purchase some Fondarific modeling chocolate to wrap around an 8" cake.  It only comes in white and I really need it to be black.  Do you think I can roll out the white modeling chocolate and lay a thin layer of black fondant on top, then wrap it around my cake so the black fondant side is facing out?  I'm afraid just using black fondant won't be a sturdy as modeling chocolate.  I thought about adding tylose to the fondant, but I'm afraid it might dry out too much and crack while I'm trying to wrap it around the cake.  

if you want to do that apply the modeling choco to the cake first get it all smoothy  smooth — it responds to the heat in your hands — then knead, roll out and apply the fondant which is stretchy and needs to be carefully smoothed — not as forgiving as the choco — get a few you tube videos under your belt first and tally ho

You could make your own black modeling chocolate.  Just use 2 packages of black Wilton's candy melts and 1/2 cup of corn syrup. Melt, stir together and turn out on waxed paper on your counter.  As soon as it's cool enough to handle, knead the excess oil out of it.  It will start out crumbly and messy but keep at it and it will come together and be smooth and beautiful. 

At this point treat it just like fondant - DON'T put it in the fridge.  Let it rest overnight and it will be ready to use. You may need to warm it for a few seconds in the microwave to get it started and keep in mind that it will get hard when it cools.  I use modeling chocolate to cover all my cakes since it tastes so much better than fondant and I can make it any color I want.

Good luck.

https://sugargeekshow.com/recipe/black-fondant-recipe/

how to make black fondant by LIzzo Marek.

Thanks for the suggestions everyone.