Traditionally, when shooting with black and white film, photographers use filters to enhance the colours in the image.
Using red, yellow or orange filters when shooting landscapes or shots where the sky has interesting detail can help darken the blues in the sky giving them more punch than they would otherwise have.
You can purchase coloured filters that screw onto the lens of a digital SLR or which can be placed over the lens of a point-and-shoot camera using an adaptor ring.
The images captured with these filters will show different conversion of colours to black and white than you would see if you were to shoot in regular black and white without the filter.
The image at the top shows two different renderings of a single image the first with a red filter and the second with a blue filter.