Originally posted by Jed
Hehe looks like I haven't been missed.
CK, when using colours with black and white film stock, the effect is not one of an increase or decrease in contrast generally, but by achieving the result by lightening the colours similar to the filter in the scene, and darkening contrasting colours. Green is sometimes used with portraits to enhance the film's response to the skin tones, and to set apart lips, etc. Red is often used to boost the contrast in the sky because it lets very little blue light through, hence "darkening" the blue parts of the sky while leaving the clouds light.