As others have said, there is no such thing as a "contrast" filter for black and white.

There are, however, filters that help you differentiate different parts of certain scenes from other parts - e.g. a yellow filter can help clouds stand out from a blue sky.

And filters that reduce the effect of UV light can also make a difference. The information above about the difference between Tri-X and T-Max when using a yellow filter is most likely due to Tri-X's greater sensitivity to UV light (which a yellow filter will tend to block).