In some cases it's possible to use workarounds like connecting
the power fractal to a displacement shader and set that to a
negative value,but that does not work for everything.
Another way can be to use negative values for buoyancy,sometimes
in conjunction with noise variation,or a color adjust shader or a
converting function and most likely there are other ways too.
Anyway,it depends on other settings aswell,so sometimes you can
get it done sometimes not,i'm afraid.
Good luck,J.
