The optional comma separated arguments are:
* ''<pattern>'' - TikZ pattern (e.g. north east lines (default), north west lines, crosshatch, crosshatch dots, grid, …) or see [[Gantt#Regressions | Regressions]] section for MetaPost
* ''<color>'' - a color of the pattern (e.g. black (default), red, green blue gray, dark gray)