def grayspec(k):
ll = <NUM_LIT><EOL>ul = <NUM_LIT><EOL>delta = (ul - ll) / k<EOL>return [GrayScale(t) for t in np.arange(ll, ul, delta)]<EOL>
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.