In a stand mixer, combine the meringue powder and water. Using the paddle attachment, beat on medium-high until the mixture becomes foamy and has a little bounce-back to it.
Remove the bowl from the stand and sift the powdered sugar into the bowl (this is important if you want smooth icing). Place the bowl back on the stand mixer and beat on low until well combined.
Stop the mixer and scrape down the sides of the bowl. Add corn syrup and extracts.
Restart the mixer and beat the mixture on medium/high speed until very thick, shiny, stiff and white. This should take about 7-10 minutes. You want the peaks of the icing to stand straight up without flopping over at all.
If you want to dye your icing just one color, you can add a few drops of food coloring into the bowl and mix it for a few seconds until the coloring is evenly distributed.
If you want to make several different colors, divide the icing into several different bowls and stir in the food coloring by hand.
Notes:Royal icing dries to a very hard consistency, and it will begin setting as soon as it is made. To prevent the icing from getting hard before you use it, thoroughly wet a paper towel and place it over the top of the icing in the bowl. It is very important to keep the icing covered! Likewise, if you are using a pastry bag and piping tips with the icing, twist the back end of the bag tightly, and wrap a wet paper towel around the tip when not in use so the icing will not dry in the tip.
Depending on the temperature, humidity, and amount of icing used, royal icing should harden within 30-60 minutes of application.