Good article on ND Filters: The Color cast issue

Hitech and other ND and GND filter tests: one the members over at naturescapes has been working on this.

Thats broadly the conclusion that Amateur Photographer, a UK weekly photo magazine, came to after they ran tests on a variety of graduated neutral density filters earlier this year. Basically none where cast free, with all sorts of weird casts, including green. In fact the cheapest, Cokin, was not the worst in their tests.

I've been using Cokins in various levels of GND and if you process them afterwords, any color cast will be gone with correct white balance of whatever you desire.

I see no reason to spend several hundred on Lee filters when Cokins get the job done just the same...I only wish I had gone Z size instead of P to reduce vignetting at wide focal lengths