White, never red.
It’s a form of art. In fact, preparing mulled wine is not unlike writing a short story where it’s all about the right details and how you place them to make one coherent piece.
Rather importantly, it has to be honey instead of sugar, the water must never boil and you should not forget a pinch of cloves. Also, it’s never red, it has to be white. And then any writer’s block will go way. Together with a headache and a dead end of another plot.