• In a saucepan, off heat, soften gelatin in cold water for 3 minutes. Put the saucepan over heat and heat just until hot. Stir to dissolve gelatin.
• Remove gelatin from heat briefly and whisk in ¼ cup of the sugar, lime juice, lime zest and egg yolks. Cook, stirring constantly, for 5 minutes. Let cool.
• While yolk mixture cools, put your egg whites and ¼ cup of the sugar in a heat-proof bowl set over a saucepan of simmering water. Using lowest speed of a handheld mixer or whisk, mix until an instant read thermometer registers 160 degrees F. Remove from heat at 160F and continue beating until soft peaks form. Do not let them get too stiff.
• In a mixing bowl, beat the softened cream cheese and gradually add the cooled gelatin mixture to it. Beat in the food coloring (if using) and fold in the egg whites and whipped topping.
• Turn into pan and smooth with a spatula. Chill until firm.

Crumb Crust

• Mix graham cracker crumbs, sugar, cinnamon, and nutmeg. Pour in melted butter and mix well. Press into greased 8 or 9 inch springform pan.