Preheat the oven to 375 degrees, and line baking sheets with parchment paper.
Cream the butter and sugar, just until smooth and combined.
Mix in the eggs and vanilla extract until incorporated.
Add the flour, cornstarch, and salt, and mix until the mixture will gather itself into a ball and pull away cleanly from the sides of the bowl.
Divide the cookie dough into four, about 145 grams each.
Add matcha powders to one of the doughs and mix well to make green dough. Then add black cocoa powder to another dough and mix well to make black dough. Add yellow gel food coloring to another dough and mix well to make yellow dough. Add regular cocoa powder to the rest of the dough and mix well to make brown dough.
Roll each dough out between 2 sheets of plastic wrap, to a thickness of about 1/4 inch.
Rest the dough sheets in a refrigerator for at least an hour. This process makes it easier to work with soft buttery dough.
Take the dough sheets out and lightly dust the surface. Cut them into shapes while they are still slightly chilled but not hard. Once the dough warms up too much, it may stick to cookie cutters. If this happens, put the sheet back in a refrigerator and repeat the process.
Bake cut-out cookie dough for 5-7 minutes. Cool completely and set them aside.