1. new wks, fill with row numbers, make 2D line plot

2. open PD dialog, go to line tab, check enable fill area under curve, click apply

3. go to pattern tab, set fill color as index: col(b), patter as index: col(b), click apply

4. set gradient fill as two colors, click OK
   ==> the whole graph is covered by pattern fill

Fixed in Origin2025.