This is a very wide subject and for some, it can be a little confusing. Not all colors are created equally and used for the same applications. So let's review this topic in order to demystify some of these products.
When talking about food coloring, you need to be aware that there are basically five different categories of food coloring. These are divided into the following:
Liquid Food Color
Gel Color (or Gel Paste Color)
Liquid food coloring is the most basic and easily accessible color, available in most local food stores. Because it is a water-based color, it is considered the weakest coloring. These types of colors are not highly pigmented and tend to be very thin. To get a vibrant color, a lot of liquid coloring would be needed. However, adding a lot of liquid coloring can alter a recipe bake time or taste and can break down products such as icings.
Ideal for: pastel shades, hand painting watercolor effects, and small batches
Water-based colors should NEVER be used to color melted chocolate as it will crack, separate, and can even spoil your chocolate.
Candy colors are oil-based colors that are primarily used for coloring chocolate and other hard candy. These colors tend to cost more than gel colors but can be just as vibrant and pigmented. Chocolate is an oil-based candy and therefore should be colored with an oil-based color. This allows for the color to be evenly saturated throughout the product and adhere to the surface.
Ideal for: chocolate melts, modeling chocolate, hard candy, and batters with high-fat content
Gel coloring (also known as Gel Paste Colors) is the opposite and much more pigmented and concentrated colors. Gel colors are ideal for almost all mediums (what you mix the color into) since less is needed to achieve a vibrant color without changing the consistency or taste of the product.
On the other hand, getting light variants of color using gel colors can be tricky as gel tends to get a bit darker as they sit and are exposed to air. Therefore, it is best to aim for a shade lighter than intended to prevent the color from getting too dark especially when you have small batches or little medium. You can always add more color in later.
Ideal for: betters, icing, fondant, marzipan, large batches
Airbrush colors are food coloring that is specifically designed to be a super thing liquid that can easily pass through the airbrush compressor machine. While some brand lines are specifically designed to be used in airbrush machines, other colors like powdered and gel colors can be diluted using a special solution allowing for a clean air stream.
Ideal for: painting or tinting both hard and soft sugar mediums
Powdered colors are pigment powders that can be used as-is or diluted to a paint-like consistency. There are many types of powder effects and finishes such as matte, hologram, metallics, and sparkly colors. These colors tend to have a long shelf life and can last for years when correctly stored. Powdered colors can be used as dry dust or paint when mixed with a high concentrated clear alcohol. The higher the alcohol concentration that is used, the faster it will dry.
Ideal for: painting harder sugar mediums
Sweet Color Lab's Dilution Solution helps turn gel colors into an airbrush solution thin enough to pass through the machine.