I don't know if you have noticed but it seems that the craft foam I've been using doesn't absorb the inks from the marking pens to readily, so I decided to use that to my advantage.
This was a yellow foam body, I took an olive permenent marker and colored the upper half. Then took a rag and rubbed the marker in to belnd it into the yellow and soften the color transition. Reapply the olive to the top 1/4 abd blend that, gradually darkening towards the top. Final application of black right along the spine and a quick blend, that's it aside from a thin coat of epoxy ( I tried the Devcon 20 minute version gently heated to flow and 'painted' it on with the side of a bodkin. Tried to get just enough to get it glossy at minimum thickness.
I need to stock up on some othe marker colors to use with the white foam, I think you could come up with some real nice blended colors.
I bought some of the "Contac" brand holographic paper at Michaels on Sunday but haven't had the chance to test it. The other source was mail order. Waiting for the UPS guy to see what the quality is like. $4.99 for 5 sheets but they had a nice selection of holographic colors/patterns.