Grdview - how to fill in frontal face with color palette


I am trying to fill in the frontal facade between the plane and my chosen data perimeter (in my case this is at the surface Z = 0km) in the grdview command. I know with -N there is the +g option to fill it in but it only works with a single color. Is there a way to fill in with a color palette?

I also explored the -Q options but the ones that fill all have m attached to it (making them monochromatic).

Here is my current code:
gmt grdview thick_ll_neg_filt.grd -JX5i -JZ1.75i -B -BSWZ -Bz30 -N-0 -Qs
-I+a225+nt0.75 -Ct.cpt -R-119/-114/32/34.5/-110/10 -p186/22

Thanks in advance for your help!

The facade is a polygon so can only be a single color