Preheat the oven to 190°C/375°F, at convection mode.
In a mixing bowl, combine the egg yolks, milk, melted butter, vanilla, and sugar. Whisk on high speed until the mixture is fluffy.
Add the flour and continue mixing until the mixture is homogeneous, then transfer to a bowl.
Clean and in a new bowl add the egg whites along with a pinch of salt. Whisk on high speed until a stiff, fluffy meringue forms.
With a spatula, take ⅓ of the meringue and fold it into the yolk mixture. Whisk until incorporated, then add another ⅓ of the meringue and continue folding. Once absorbed, add the remaining meringue.
Divide the sponge cake batter into 2 bowls, adding red food coloring to one and green to the other. Mix with a spoon and transfer the two mixtures into separate piping bags.
Line a baking tray (33x20cm or 13x8 inches) with parchment paper and alternate spreading the mixtures diagonally. Bake for 12 minutes.
Once baked, transfer the sponge cake while warm onto a towel dusted with powdered sugar. Roll the sponge cake with the help of the towel, starting from the long side.
Set the rolled sponge cake aside to cool completely.