from typing import Optional


def get_colour(label: str) -> Optional[str]:
    """Given the label of the thing to plot, determine the colour."""
    if "given investment" in label:
        return "orange"
    if "all-in day one" in label:
        return "blue"
    if "cash" in label:
        return "red"
    if "nominal account" in label:
        return "magenta"
    if "account" in label:
        return "green"
    return None