A long time ago, about bryce 3 I think, I had a mat which I could apply to a torus and get a rainbow which I could then place wherever I wanted it.

Of course I no longer have that mat, and after many tries cannot work out how to make a similar rainbow.

Does any one have any idea how I can go about doing this.

I tried uv mapping a torus, which does work, except that i can't alter the torus as you can bryce ones, so my rainbow is too thick.

The greatest part of wisdom is learning to develop  the ineffable genius of extracting the "neither here nor there" out of any situation...."