If I use two polarizers (see here for details), things vary a bit: At maximum extinction, the resulting picture is defacto greyscale. If I dial in more colour, I usually want to have that colour in the picture - so no postprocessing.
Sometimes, my 2040 still has some colour in its shots when using my Heliopan 715nm filter. Here's what can be done then:
Manual white balance on foliage. Late afternoon, just at the beginning of sunset:
ISO speed: 100
Focal length: 7.3000
Then: Swap red&blue, manual levels, saturation adjustment to get a blue sky. USMed. Easy. (It looks a bit oversharpened when resized.)
Another example (take your preference...)
Auto-Smart-Fix in Photo Shop Elements 3.0
Manual RGB-histogram adjustment and blue&red swap similar to what Luben Solev recommends.