Prime the model white, then slather with yellow ink (mixed with a tiny bit of dish detergent).
This is going to be my second Fire Prism. I wanted to make the Fire Prisms in my force to be an exception to my usual technique of Bone Undercoat + Blue Accents. I wanted to make them more solid colors, just to give them some distinction from the look of the Wave Serpents.
I'm challenged to come up with fresh angles on certain paint schemes, as my goal is to at least prime and base-coat everything in my possession. I have a strong aversion to having unpainted, unassembled models just sitting around. My hope is, before long, every model I own will either be in service or it'll be sold/given away/donated to the cat to play with.
More on this as it develops.