I would ask the customer for a color swatch so you have something to match with.
I had to make Sangria icing for a wedding cake last year...it's the weird alice in wonderland style wedding cake. I didn't color fondant but I am assuming you would work with the same colors. I am pretty sure I started with americolor gel in maroon. That gave it a red/purple type color, and then I added some fuschia. It was hit or miss and it took me a WHILE to mix that icing to the exact color of the David's Bridal swatch, but I think I did pretty good. All in all, I think I ended up using mostly maroon and fuschia, and a little bit of burgundy. All americolor gel colors.
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