I think you can get a chemical blackening agent for SS, but can't remember where I saw it at. You might try Triple S Chemical or Sculpt Nouveau, they'd probably know what options you have.

Jake

Jake Balcom
Mettle Design
Lincoln, NE

I would use some lights on the stainless, with red and amber lens, perhaps even with a motorized color wheel. You might want to design your own lens for the motorized color wheel so you are projecting an ever changing mix of yellows and reds. Then the sculpture can be polished to reflect those colors. You may even want to add some elements a few inches forward of the focal point, powdercoated Red, Orange and Yellow on the side facing the sculpture main feature, and polished stainless look on the side facing the viewers.
Best wishes,
Stephenkishel.com

i've often done designs on stainless with a tig welder, and accent them with a oxy acetylene heat torch...

i did some flames once on a peice of scrap rolltop, i tig'd the surface of the peice and 'painted' them with the torch... tiging the surface leaves you with a welded bead, if you don't want this bead tig the underside.. but the color is a bit duller on the underside of the weld.

the tig brings out pretty brilliant colors, but becareful of warpage/oilcanning.

as for the just leaving the fire look, painting like the top part of the sculpture and then burning that off, maybe a few layers... that sounds interesting.