>>3954443Colour film has both silver halide crystals like B&W film and these dye couplers which develop alongside the silver when subjected to the developer soup.
When you then bleach the film, it reduces the developed silver back into its original halide. This, followed by the fixer, removes all the silver and leaves behind just the layers of dye.
Skipping the bleach means when you fix, the developed silver sticks around. So you now have a colour and a B&W image mixed together which has the effect of reducing saturation and increasing contrast and grain.
Saving Private Ryan is one of the most well-known film films to use bleach bypass to create that gritty, ugly aesthetic of the battlefield.
