Just got myself some cokin nd's and a circular polarizer and after doing some test shooting I noticed that it exhibits a look that has become fairly familiar to me after watching many dslr videos online. Its not a bad look, but its not a natural or vibrant look either. If I want this look I would rather achieve it in post production.

I cant put my finger on exactly what it is.

Seems to be a slightly desaturated look, but coupled with a polarizer perhaps it is only on some colors. ie reds still stand out.

Narrow depth of field in bright sunlight? I was shooting at 1.4, 50fps in sunny conditions, maybe there is just something unfamiliar/wrong about how this looks

Infrared? I have heard that infrared can go out of balance when using ND filters. Tiffen might be the answer to this.

I'll be trying it next time I shoot, but would a manual color balance account for infrared and and other color casts casts resulting from ND's?

Already looking beyond cokin at matte boxes and glass filters but they will have to wait a few more pay days.

You may find that the particular NDs you're using do give a colour cast, i.e. they're not neutral in colour terms. Some filter companies make filters which don't give you this, however, they are more expensive eg:

https://www.schneideroptics.com/ecommerce/CatalogSubCategoryDisplay.aspx?CID=445

The IR becomes an issue when you use dense NDs eg 1.2 or greater on some cameras.

sure, I was using a nd8 (0.8 I think) plus a polariser which seems to be similar to a 0.3 or 0.4 nd, also a grad .4 so was certainly beating 1.2. I tried the .8 grad, it made the sky red as I slid it in.

I've just done a quick google, it seems Cokin NDs are well known for having a colour cast (seemingly magenta).

yes, I've read lots about that. Did some tests today in bright (winter) 1pm sunshine on people. ND8 plus ND4 plus polarizer got me down to 50fps at f1.8 Skin tones rendered the colors of blood oranges on auto wb. I definitely think that IR is a big issue with this much filtration.

The good news is a custom white balance with the filters on helped dramatically. I used a white piece of photocopy paper that probably was a little bit cool/translucent. I imagine with something slightly warmer and more solid, like a whiteboard, results would be better again.

Perhaps someone with more knowledge on color correcting can tell me. Is it easier to warm things up or cool things down in post production?

Using an IR reduction filter is common on quite a few cameras that are sensitive to these wavelengths. For example, the RED camera is one camera that needs it when using denser NDs. It's especially a problem with black objects that radiate more IR.

Here are some IR filter tests on high end cameras.

http://provideocoalition.com/index.php/aadams/story/ir_cheat_sheet_version

I've just done a quick google, it seems Cokin NDs are well known for having a colour cast (seemingly magenta).

Yes, that's true. I bought a graduated ND from Cookin and to my surprise it had a magenta color cast. If I would have know this before I wouldn't have bought it! This fact makes it difficult to use these filters in a lot of situations... I'm interested in how other people coupe with this problem??