Sounds like you know your stuff George haha, I'd love to see some examples if you have the time :)
I hope this will help clarify my approach, as mentioned previously it depends on the method used, for electrolytic coloring with metal salts being used as colorants your coating/film will consist of metal coloring (limited to colors with yellow tints, blacks, bronze or gold) deposited in the oxide pores.
As to how to approach this with Corona Physical and make it as accurate as possible, you can start with an aluminium foil preset as base from the Basic options > Apply preset of Corona Physical material, these presets are all made using Complex IOR for metals, so their parameters are physically accurate. You will need to create a Corona Layered Mtl. and set your base as the aluminium foil, for coating you will need to create a metal material as an electrolytic dye and apply it in your layer slot, you can either "eye-ball" it or use complex IOR to get more physically accurate results (please refer to the guide here:
https://support.chaos.com/hc/en-us/articles/4528348723985-How-to-use-ComplexIOR-for-CoronaPhysicalMtl-) (do note you can do this with clearcoat as well but you are missing out on complex IOR properties of the coating).
For organic or inorganic dyeing/coloring that mostly consists of chemical dyes, you will need to create a Corona Physical Mtl. with an aluminium foil preset as base from the Basic options > Apply preset of Corona Physical material. Enable your Clearcoat layer set the corresponding IOR of the coloring agent that's being used (f.e. acrylic), and simply allocate the color of your choosing. For both cases surface irregularities might be bound in both the coated material but also the base depending on what you want to achieve as for color-intensity/saturation it really depends on the process. I am attaching some really basic examples/images!
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