Wilton makes a professional food color that is perfect for the home baker. I have always used Wilton's gel food coloring because the colors are so much more vivid and easy to control than they are with liquid food coloring. They come in 1/2 ounce jars and you can get them individually or in sets. I have the 8 color set that includes Christmas Red, Leaf Green, Sky Blue, Lemon Yellow, Brown, Orange, and Violet. For those that might keep a Kosher kitchen, these food colors are certified Kosher.
We make a lot of cakes in our household because my daughter has a cupcake business. We always use Wilton's colors to color the frosting of the cakes. You only need a little bit of the coloring to make very bright colors. Just dip a toothpick in the coloring and add to the frosting.
We use the food color for other things besides icing. We color some of the cakes and it works very well. We also use it to dye Easter eggs and added a little of the gel color to some vinegar and hot water and it made very vivid eggs.
Some people complain that the color changes once you get it on the cake and the cake gets in the sun. I have never had that happen and have been using this food coloring for a long time and my mother used it before me. I'm not sure what they are doing wrong, but my color is always true and stays that way.