Preheat oven to 375 and grease a 9x13 baking pan (if you have that size of baking sheet that works too).
In a medium mixing bowl, combine flour, salt, and soda and set aside.
With an electric standing mixer, cream the butter and sugar together until light and fluffy. Add one egg at a time and then add the vanilla. Add the dry ingredients and mix until almost combined. Take out half the dough (you can put it in the bowl the dry ingredients used to be in).
With the dough left in the bowl of the standing mixer, add yellow food coloring (I like the gel kind). Mix until evenly mixed in. Spread evenly in the bottom of the prepared pan. I recommend dropping the dough on the pan in globs and then spread. Scrape out as much of the yellow dough as possible.
Put the bowl back in the mixer and mix the remaining dough with orange food coloring (or yellow and red to make orange). This is trickier to spread so you definitely want to apply the dough in spoonfuls evenly over the yellow layer and then just spread out each little glob of dough until the surface is smooth. Pop it in the oven for 13-16 minutes or until a toothpick comes out clean and when you press on the surface it springs back. Allow to cool completely.
Beat butter and cream cheese together until smooth and creamy. Mix in vanilla and then add the powdered sugar a little at a time (don't want a powdered sugar dust cloud!). Add milk to reach desire consistency and beat until combined.
Apply frosting to cooled cookie in an even layer. Add sprinkles or candy corn if desired.
Cut the bars into 4 even rows and then cut out the triangles (6 per row). I made mine have a 2 1/2 inch base and actually got my ruler out to make it exact. You will have two half triangles when you cute each row which are great to munch on (or give to the kids) while measuring and cutting the rest of the triangles.