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Can any one tell me how to mimic Cokin vari-colour filters.
As in their filter numbers 170 through 173.

The actual filters are linear polarizers and I have had some problems using digital cameras whith linear filters (ND, etc..).

There are some plugins that let you do that. One of them is at
http://www.chromasoftware.com/photographic_filters.htm

Cokin Vari-Color filters change similarly but vary between two colors, could a person vary two layers and combine them to achieve the same effects?

Red/Blue--Purple/Orange--Blue/yellow--etc..

These filters are made to be used with a neutral polarizer and that adds another dimension. Polarizers do more than just add contrast but may be adding contrast would help.

Reflections are also varied but that is something that may not be able to be done in software?

It appears that the Pola-Color filters are the same only with one color.

If I had the book number/publish date, Cokin published I could reference the pages that show what I mean. The Guide to Cokin Filters 106 pages, 454 examples with a Blond lady's picture surrounded by other pictures is the best example of what I mean.

Yes, you can simulate such filters with layers and the gradient tool, too.

Software cannot influence reflection phenomens. You need to use a real glass filter for that. A software polarizer only imitates the color/saturation of a real polarizer filter.