I recently made a cake for valentine's day, and I was wanting to decorate it with a black and rose-red fondant. But when I went to dye the fondant, I could only get it to turn out grey and pink, even though I used the Wilton Black and Christmas Red coloring pastes. What do I need to do to tint fondant a deep rich color?

Yes - ditch the Wilton colors and get some Americolors. Other people here also recommend the Decopak gels and Chef Rubber products. I've had outstanding results for years with Americolors and haven't tried any of the other brands (yet).

You just didn't add enough color to your fondant. Next time, try starting with a dark chocolate fondant and then it won't take nearly as much black color to achieve a deep, rich black color.

Those are very hard colors to achieve in food products.
Cakepro is right......besides what she said, CountryKitchenusa.com has (I think it's) ChefMaster colors.
They must be made at least the night before or longer before wanting to use.
Also, fondant colors dry a little lighter than when they go on.
Starting from white is always harder. If you want red, color it orange, yellow or deep pink 1st, then add your red.
These same rules apply to these colors when using any icing.

I disagree with having to wait overnight for deep colors to develop. I've never had to wait overnight for the color to deepen into the shade I want...it's more like half an hour.

If I had to wait overnight for my icing to get to the right shade, I'd be in a lot of trouble. LOL

Also, if you start your red with pink, orange or yellow, you may not end up with the exact shade of red you want. If you start with orange, for example, you will end up with a red that is like the Campbell's soup label color.

Seriously, just get some good colors and sock the color to the fondant. This is what I do all the time and have never been disappointed in achieving red or black fondant or gumpaste.

Buy it! You can't beat the rich bright red and perfect black found with Satin Ice! Super easy too!

I used to use color...but, to get a really rich deep color you use a lot of paste. And sometimes the fondant begins to get sticky to get this deep color. I buy Satin Ice red, black purple etc. so, quick and so easy and with the time and money you save on the paste and kneading time, it is worth every penny.

I love black Satin Ice! It's well worth the investment. I've always had difficulty getting a good black color when I started with white fondant, even when starting with darker shades and working into black. More often than not it looked like it was going to be black, but then it would fade, sometimes to a greenish tone and so I finally gave in. Satin Ice rocks plus the taste is good. A little sweet but much better than most commercial fondant.

I have to give a shout out to Satin Ice fondant. I love the taste and the Black are Red are fantastic shades. I have gotten a little lazy and also bought the purple and green. It just saves time when it come to decorating.