It's all about ink (toner for your laser copier) and paper.
Color copier manufacturers recommend a brighter quality paper of heavier stock (24 or 28 pound rather than the normal 20 pound) which will add to your per copy cost.
When it comes to ink or toner, the color copier requires more cartridges than the simple black of a monochromatic copier. Four toner colors (cyan or blue, magenta, yellow and black, known compositely as CMYK) mix to produce all the colors necessary for color copying. These toners can run over $100 per cartridge in a laser color copier. For an inkjet model they vary from $12 to $60 depending on manufacturer and ink capacity.
Then there is developer, which mixes with the toner to adhere to the copier drum. Each toner color requires a developer whose life is about double that of the toner. Lasting twice as long as the developer is the fuser oil. The copier drum is also in many cases considered a consumable and run over $100 each.