Preheat your oven to 250°F. Line two baking sheets with parchment, or lightly grease and flour them. If your baking sheets are dark, nestle another pan underneath it to create a layer of air, which will minimize dark-bottomed meringues., In a medium bowl combine the two sugars and set aside., Place the room-temperature egg whites into the bowl of a mixer. Add the cream of tartar. Beat on slow speed until the cream of tartar is dissolved and the egg whites are foamy, about 2 minutes. Add the salt., Slowly increase the speed of the mixer. When the volume of the eggs has doubled and they begin to look opaque, sprinkle in sugar by the tablespoon. Continue to beat, until the whites are glossy and getting stiff. Slowly (over 4 to 5 minutes) add the remaining sugar and mix until it's evenly distributed and the whites hold a stiff peak., Fold in the flavoring and coloring of your choice, and nuts or chocolate., Drop the mixture by the tablespoonful onto the prepared pans, or fill a pastry bag and use it to pipe out any design you wish. Top them with more nuts, chocolate, sparkling white sugar, sprinkles, or other decoration., Place the meringues in the oven. After 30 minutes, reduce the oven heat to 225°F, and continue to bake for another 1 to 2 hours. For a chewy meringue, bake for the shorter time (about 1 hour). When the cookie is finished, its center will measure 165°F on an instant-read thermometer. For crunchy meringues, bake them for the longer time (about 2 hours). To test if they're done, pick one up; it should feel very light. Tap the bottom; it should feel hollow. Break one open; it should be dry. Taste the broken one while it's still warm; it should melt in your mouth. When the meringue is finished it should be almost white, with just a hint of color around the bottom. Turn off the oven, prop the door open and allow the meringues to cool on the pan in the oven for 30 minutes., Remove the meringues from the pans, and place them on a wire rack to cool completely. Store in airtight containers for up to several weeks.