The following is a side by side comparison of two images both taken with a Tiffen Haze-1 filter, and one using a Cokin 154 Grey Neutralizer filter. Both photos were taken using an ISO/ASA setting of 500 with a Pentax K-x DSLR using a SMC Pentax-M 1:2 50mm lens @ F/2.
This first image is using the Cokin Grey Neutralizer and Tiffen Haze-1 Filter.
This next image is using only the Tiffen Haze-1 filter.
Shadowing in the image using the Grey Neutralizer seems to be slightly softer, and there is also a slight dulling of colour.