Summarize the following:
Unless your heart is set on vanilla, go with a chocolate icing. Starting with a brown-colored icing means you have to use less dye to achieve a black hue.  You can still start with a white icing, but you will probably have to add flavoring later to cover the bitterness of the dye. You can dye most icing--including buttercream, cream cheese, or royal icing--black by following these instructions. Because royal icing is white, you may need to add flavoring or cocoa powder to hide the bitter flavor. You may be limited to what they carry at your local grocery store, but if you have a choice between liquid or gel coloring, choose the gel. You will use less of the gel than you would the liquid coloring. If you cannot find black dye, mix equal parts red, blue, and green food coloring. You won't get the "true" black like you would from the store-bought black, but you can achieve a very dark gray that can pass for black. Adding the dye (especially liquid) may thin out your icing, which can lead to bleeding. Store-bought icing will probably be a fine consistency, as it is usually nice and thick.  To thicken, thoroughly mix in some sifted powdered (aka confectioner's) sugar.  If you don't want your icing any sweeter but it's not thick enough, add some meringue powder instead.  If you are using royal icing, drag a butter knife through the surface. Count how long it takes the icing to smooth back over. If it's between 5-10 seconds, your icing is thick enough. Any faster and you need to mix it longer or add a little sifted powdered sugar or meringue powder. The black dye may stain plastic. You may also want to wear an apron so you don't get any dye on your clothes. You will probably end up using a lot of dye--sometimes up to 1 oz or a teaspoon of coloring per cup--but it's better to add it gradually so you don't accidentally overdo it and end up with runny or splotchy icing.  Black icing can make your icing bitter and unpalatable. If this happens to your icing, look at section two (Addressing Common Problems) to learn how to cover the bitterness. If you are close to black but can't seem to get past a dark gray, give your icing a few hours to develop. The color will deepen over time, and in as little as one hour your dark gray icing can turn a rich, complex black.  The color will continue to deepen even once you've piped it onto a cookie or cake, so if you are super short on time you can go ahead and decorate immediately. Just be aware you won't have the opportunity to troubleshoot if the icing doesn't develop into the black you want.  Keep the icing out of direct light as it develops, as this can cause the black to fade.

Summary:
Buy or make your icing. Choose a black food coloring. Thicken your icing if necessary. Transfer your frosting to a large glass or stainless steel bowl. Add black dye to your icing a little bit at a time until you reach the desired shade. Mix dye thoroughly so there are no lumps or streaks in your icing. Taste the icing. Cover your icing and let it sit. Decorate your masterpiece!