C-41 film is the most common color-negative film and when viewed, the negatives will appear orange with the darkest spots of the image appearing light (negative). C-41, E-6 (positive color slide film), and K-14 are designations created by film manufacturers to define different types of film and the developing process. It's not necessary for the photographer to know this code, but it tells the lab how to process the film - what chemicals to use, what temperatures, and what timing.