I use the AmeriColors Super Red and it works great! HTH
I agree - Super Red from Americolor is great. BUT, it's still hard to get white fondant a good, true red without applying a lot of color. I would recommend that you buy red fondant and save yourself some trouble.
I've also been successful in using hot pink fondant and adding red to make it a strawberry shade of red.
I agree with Motta - buy some ready made fondant in red - if you want to make flowers buy the gumpaste already red or add some tylose to the red fondant. I use sugarflair paste colours in poppy red and christmas red if I need to colour some from scratch
Deep, dark colors are hard to work obtain.
One cannot expect instant perfection of a dark, deep shade of any color.
Red is a very difficult color to obtain. There is only so much the makers of food colors can do legally.
As others have said, it sometimes will take a combination of tints to reach what you are looking for.
Fondant and/or gumpaste are different than buttercream - easier really 
If you tint the white fondant/gp (or buttercream, too) either yellow, pink, or orange it will take far less *SUPER* red to get a nice red shade.
And........do use any food coloring that has the word 'super' on it for those intense colors.
Make a special effort to get AmeriColor gels whenever you are ready to replace your colors I also have had excellent results from Cake Craft brand and any liquid gels.
Oh, and one more thing: Don't be too concerned if you don't come up with the perfect shade. Fondant/gp flowers are very much improved when petal dusts are used to highlight them. It will bring out the color used to make the petals. When you look at nature, you find the colors are seldom perfect, totally the same. There is usually slight shade/tone differences. Using dusts gives you that look.
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