Final answer:
To achieve dramatically lighter hair color, use bleaching agents such as hydrogen peroxide (H₂O₂) mixed with aqueous ammonia. Semi-permanent hair color cannot lighten hair.
Step-by-step explanation:
To achieve dramatically lighter hair color, you would use bleaching agents such as hydrogen peroxide (H₂O₂) mixed with aqueous ammonia. Bleaching is a chemical process that lightens the hair by removing its natural pigment. Permanent hair color can also be used, which involves altering the hair's structure chemically, but it is important to note that semi-permanent hair color cannot lighten hair.