Preheat oven to 350 degrees. Spray four 8 1/2 inch round pans with non-stick cooking spray and add 1 tablespoon of cocoa powder to each pan. Move the cocoa powder around to cover the pans and tap out the excess into the next pan or into the garbage. Feel free to use regular cocoa powder for this.
In a mixing bowl, add in the vegetable oil and sugar. Mix until incorporated.
Add in the vanilla and one egg at a time until incorporated. Once incorporated, add the next egg.
In a large measuring cup or bowl, add in the cold buttermilk and strong coffee. The cold buttermilk will cool down the coffee if it's hot. Set aside.
In a large bowl, add in the flour, cocoa powder, baking soda, baking powder and salt. Mix to combine.
Alternately add the dry and wet mixtures into the vegetable oil and sugar mixture starting and ending with flour. I broke mine into flour 4 times and buttermilk 3 times. Scrape down the sides and bottom and mix for additional 30 seconds. If you want the cake darker, add the gel paste color in with the last addition of flour.
Pour 3 of the 4 pans 3/4 full of batter. In the last pan, add enough batter to cover the bottom of the pan.
Place the 3 pans that are 3/4 full in the oven and let them bake for 35 - 40 minutes or until done. To check, place a toothpick in the center of the cake. If it comes out with batter on it, bake it longer and check it again. If it comes out clean or with moist crumbs, it's done.
Place the 4th pan in the oven and bake for 15 minutes or until done. Check it the same way as the first 3 pans.
Let the cakes cool completely.
In a mixing bowl, add in the butter, powdered sugar, milk and vanilla. Mix on low until almost combined. This will help prevent powdered sugar from flying all over.
Once everything is nearly combined, add in the electric green gel paste color and turn the mixer on high and mix about 2 minutes.
Black Chocolate Frosting
In a mixing bowl, add in the butter and cocoa powder and mix until combined.
Add in the powdered sugar and milk and mix until incorporated.
If you want it darker, add in the black gel paste color. Mix on high for about 2 minutes until light and fluffy. If it's too thick, add another tablespoon of milk.
Prepare the fluff after the cake is frosted.
In a sandwich bag, add in the fluff and green gel paste color.
Heat in the microwave for 30 seconds and squish the bag around to color the fluff. The bag will be pretty warm so be careful.