i have to make a black graduation cap and thought it would be no problem! 
well...i started coloring my white fondant/gumpaste with black and it's not working...it's coming out purple!!!! 
what is going on??? i've done black fondant before...and can't seem to figure out what is happening!!! is it the humidity...the coloring...what???
any help would be more than appreciated!!! 
Instead of starting on with white it is easier next time to add cocoa to the white fondant/gumpaste to give it a brown colour and then add the black colouring and it will save you time and colouring and will give you your black.
Also let the fondant sit out overnight to let the develop the colour and it is usually darker the next day.
i did this once with a graduation cap and scroll cookie (it's in my gallery) and it worked perfectly and gave me a nice strong black colour.
HTH 
I found Cake Craft paste color in Super Black. Added a bit of brown color to white fondant, then added super black. You will see a bit of purple, but i kept adding black and it came out nice. i have it on a a zoo pic in my gallery. i liked it so much i bought the super sized jar.
Hi diane I took a color class some time ago what you have to do now because you have the purple fondant just add some gold or yellow to it and that it is going to neutralize the purple and you will have like dark brown color the add black and you are going to have a really nice black.
What I do to make black fondant or icing is I start with chocolate fondant and then I add the black and let it rest for couple hours if you do not want the chocolate flavor color it brown and the add the black 
Here is the color wheel
i am going to give that a try. hopefully i can salvage my fondant. 
It can be the brand of fondant you are using. I did a class once where we used a type of fondant which would not go black with regular colouring, it went green. We had to use powdered black food colour to get it to go properly black.
Also you will need a lot more colour than you think to get a true black, you just have to keep going until you are there. It is also a good idea to let the fondant sit for a while to let the colour deepen.
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