One of my friends wants a Lightening McQueen cake for her son's birthday. How do I get that red icing and not pink? How much of which red should I use?
Thanks!

Do you use the paste kind? I usually use a lot of red, also make it up 2-3days ahead because it will get darker,

I prefer Americolor Super Red which will get you a good bright red. I agree with mixing a few days ahead to allow the color to darken. If you add enough color to make it the red you want right now, it will be too much color after a few days, and may start to pool on top of the buttercream.

Many years ago, I actually had a Santa cake "bleed" color when we had leftovers the next day, because I had added so much color right before I decorated. I make 4 cups of red at a time (also royal blue and black) and allow it to "rest" a few days on my kitchen counter before first use. I start with 60 drops, which equals a little more than a teaspoon. You can always add more if it's not dark enough, but only after it has a chance to rest. I stir it periodically to distribute the color well.

After the resting period, I store it in the fridge and only take out what I need. The last bit of it is always much much darker than the first portion I used.

I use the Wilton gel coloring. I have Christmas red and Red red. Which one would be better?