Coffee cake with coffee buttercream + blue buttercream recipe

Ingredients : Coffee Sponge Cake Eggs 5 (Separate white and yolks) Granulated fine sugar ⅓ + ½ Cup Warm milk ⅓ Cup + 2tsp Instant Coffee Oil ⅓ Cup All purpose flour 1 ¼ Cup Cocoa Powder 2 tbsp Baking Powder 1 tsp Salt ¼ tsp Coffee Buttercream Hotmilk 2 tbsp + 2tsp instant Coffee Unsalted soft butter 200g Icing Sugar 100g Sweetened Condensed milk 80g Blue buttercream Unsalted butter 200g Icing sugar 400g Vanilla essence few drops Colors required; 1-Royal Blue 2-Black 3- Violet