List of gray-scale colors in HSV space as web hex triplets.

    For integer argument k, returns list of `k` gray-scale colors, increasingly 
    light, linearly in the HSV color space, as web hex triplets.

    Technical dependency of :func:`tabular.spreadsheet.aggregate_in`.

    **Parameters**

            **k** :  positive integer

                    Number of gray-scale colors to return.

    **Returns**

            **glist** :  list of strings

                    List of `k` gray-scale colors.

def grayspec(k):
    """
    List of gray-scale colors in HSV space as web hex triplets.

    For integer argument k, returns list of `k` gray-scale colors, increasingly 
    light, linearly in the HSV color space, as web hex triplets.

    Technical dependency of :func:`tabular.spreadsheet.aggregate_in`.

    **Parameters**

            **k** :  positive integer

                    Number of gray-scale colors to return.

    **Returns**

            **glist** :  list of strings

                    List of `k` gray-scale colors.

    """
    ll = .5
    ul = .8
    delta = (ul - ll) / k
    return [GrayScale(t) for t in np.arange(ll, ul, delta)]