Why is the hair of Howl was colored black when he was young?
Sophie went and organized his hair coloring products (like he said not to) Howl's hair is naturally black he dyes his hair blonde. When he rushed out of the bathroom this hair was a bright orange because his products weren't in the order he was used to, so by instinct he chose the wrong bottle. When he got depressed because he wasn't "beautiful" his hair turned into it's natural black color.
Because his hair is naturally black, in the vision she saw, his hair is black, not blonde.