The Black & White tool allows you to convert
a color photo into a black-and-white photo.
Additionally, you can control the conversion as if a colored filter were placed in front of the lens when the photo was taken.
Note: A filter of a certain color actually filters out its complementary color (the color directly across from it in the color wheel).
For example, a yellow filter filters out blue light (because blue is directly across from yellow). Therefore, you can usually increase contrast in the sky by using a yellow filter because it filters out the blue of the sky thus making the sky darker compared to clouds.