import re


def determine_color_label_index(item):
    """
    Returns a number >= 0 if the given item is a color label (aka Collection),
    -1 otherwise. The number represents the index of the color label in the list of
    *all* color labels (i.e. including currently invisible/disabled labels)
    """
    match = re.search(b'^color:colors=(\\d+)$', item.uri)
    is_color_label = match is not None
    if is_color_label:
        return int(match.group(1)) - 1
    else:
        return -1