All ingredients ready? Let's begin!
Preheat your oven to 350F. Grease two round 8 inch cake pans with butter and a little bit of flour, making sure to cover the sides as well.
In the bowl of a standing mixer (or, if you don't have one, in a regular mixing bowl) add the butter and sugar. Beat with the paddle attachment until light and fluffy.
Slowly mix in the eggs one at a time, beating well after each to incorporate.
Add the vanilla and mix until incorporated. Do the same with the rum.
Zest the outside of the orange and lemon then add both to the sugar-butter mixture and mix until combined.
In a new, clean bowl, add the flour, baking powder, and salt. Whisk to combine.
Slowly add the flour mixture bit by bit to the sugar-butter mixture. Make sure to carefully mix between additions.
If you want to use food coloring for your cake, now is the time to do so.
Separate the batter into a few different bowls and add a couple drops of different food colors to each. Mix each color into the batter until it reaches the desired shade (add a few more drops of food coloring if needed).
If not using food coloring, divide the batter and pour half into each pan. Use a spatula to scrape all the batter out of the bowl.
If using food coloring, alternate swirling the different colors into each pan, using roughly half for each. If you want, use a skewer or chopstick to further swirl the colors in the pan.
Put the cake in the oven for 45 minutes. Check after that with a skewer or fork. If the skewer comes out with batter stuck to it, it needs more time. It may need to cook for a little over an hour.
Once you can insert and remove a skewer without having batter stuck to it, remove the cakes from the oven.
Allow the cakes to cool for at least half an hour before turning them out to continue cooling on a rack. If the cakes stick to the pan, run a knife around the edges and try again.
Let cool before serving.