Does anyone know of or have an idea of how to create a Superfly shader for an oil slick? You know, when the black oil is hit by sunlight and has that rainbow effect? Thank you for any assistance!

The only person I know is bagginsbill. However, it may require very many nodes to get the effect you want at the expense of certain compromises. Off the bat, I looked for a blender cycle node arrangement and the first thing mentioned is that it might not be possible. But one example of a shader arrangement revealed certain nodes that don't exist in Poser. Let see if bagginsbill actually sees this post and responds.

OK, here's what I use for iridescence, which covers refractive/reflective/prismatic effect in thin layered materials, such as oil, soap bubbles, mother of pearl, sequins, etc.

Here, in SuperFly, we're using a specular only material. Lowering the brightness (the white colour chip in either alternate specular or the compound metal node will give iridescence on oil, with reduced reflections.

Adding some white diffuse to the shader gives mother of pearl.

Removing the diffuse again, but reducing the IOR from 20 (which is a bagginsbill discovery for reproducing the effects of complex IOR in metals, vs dielectrics) to 1.45 for glass, gives a soap bubble effect.

Apart from bagginsbill's metal shader techniques, which are awesome, the key to iridescence is the HSV node. Since the hue input values revolve around the ROYGBV circle, multiplying the hue by a large integer and feeding it from the Fresnel node, which addresses angle of incidence at the sphere's surface, gives an adjustable band of rainbow hues.

Missed one. Had to play with the angles and flatness to get sufficient reflection. Colour chip is 10% value grey. Here's an oil puddle:

Oh, I should mention, you can ignore and omit the HSV node plugged into PoserSurface:Specular_Color. The idea was to be able to see what the hues would be in a preview without rendering, but it's turned off here and does nothing at all.

Much of this is fakery of the first order. You'll notice there's no connection between the IOR in the Fresnel_Blend node and that used for the surface reflectivity. Feel free to adjust the Fresnel_Blend IOR to your taste, as it only affects the rainbow banding. The soap bubble isn't showing real refraction. If you changed the GlossyBSDF nodes in the Compound_Metal shader for GlassBSDF, you could play with different results including refraction. But remember, a soap bubble is a thin membrane, so you'd really want two nested spheres to represent the inner and outer surfaces of the bubble.

Have some iridescent sequins:

@an0malaus

Thank you so much! I'll try your settings and see what I can come up with. :)

Do you mean a shader like this?