Most supermarkets carry one basic type of food coloring, a water-based liquid that comes in red, blue, green and yellow. This type of food coloring works pretty well for most purposes. You can dye Easter eggs with it, get creative with cake batter colors and even add it to drinks to make things like plain milk a little more “interesting” (which I did as a kid). But when you are aiming for a really intense, vibrant color – such as the signature red of Red Velvet cake – food coloring can cause a lot of frustration because you need to add a lot of it to get that much color. This isn’t a problem for most recipes, as a tablespoon or so of what is basically water isn’t going to hugely impact the outcome. But for some recipes, it can negatively impact the recipe (with too much liquid/throwing off the consistency) as well as give you a headache as you try to figure out how much to add.
I like to use gel food colorings for this very reason. These food colorings, also sometimes called icing colors, usually have a corn syrup and/or glycerine base and a much, much more intense color than regular food colorings. You don’t have to use nearly as much coloring – sometimes only a few drops – to get the same color effect (or better) as you would with several times as much regular food coloring. Less liquid means that these colorings will work better in candies and frostings, where the amount of liquid in the final recipe can be quite important. Since you use less, I find that these last longer than other colorings, too. You can find them online and at craft stores (sometimes kitchen stores carry them, as well) and they often come in more colors than the plain variety from the market.