The differences between colour and mono (black and white) laser printers is in the toner and drum mechanisms. A laser printer works by using a laser to create an electrical charge pattern on the drum. This is then used to pick up toner, and roll it across the paper. Where a black and white printer does this once, a colour laser printer will do this once for every colour that's being placed on the page, and will interpolate different spots of different colours of toner to make different hues and shades.

What this means is that for a colour laser printer, there's a greater series of expendables to be had - you have to buy anywhere from three additional colours of toner (for Yellow/Magenta/Cyan) to six different colours for high end photo-lithographic colour laser printer.

Most of the additional expense of colour laser printers has come from the added wear and tear on the drums in the mechanism; the typical laser printer drum in a desktop printer used to be good for about 20,000 impressions before it would get worn to the point where it wouldn't release toner (this is why worn out drums tend to leave streaks of lighter printing down one side or the middle of a sheet of paper).

Advances in drum technology have increased considerably on the higher end printers - many now have drums that are good for half a million pages or more…however, with colour laser printers having to do a separate pass for each colour laid down, the general rule of thumb is that a colour drum will last for about a quarter as many printed pages as a black and white printer's drum would.

What these advances in drum durability mean is that colour laser printers have become significantly less expensive to purchase, and they've generally become cheaper to operate, as the number of vendors producing colour toner sets has increased, driving the prices down. As a result, they've moved from 'high end office equipment' to 'most businesses will have one' and are quickly making their way down to the consumer end of the market as well.

If you're looking for a colour laser printer, understand that there's a clear demarcation between 'business colour' and 'photographic' or PANTONE colour. In an effort to retain premium pricing on the devices, the manufacturers are adding capabilities, but most of the inexpensive models have relatively unsophisticated colour gamuts, which makes them good for printing, say, letterhead reports or pie charts, but will get noticeable flattening of colour reproduction when used for photographs or similar items where subtle shadings in hue are needed.

That being said, many of them are now at the point where the cost of printing a colour page with modest amounts of coverage (about 15% to 20% of the surface in color) are only two to three times as expensive as printing a black and white page from a dedicated printer. Even full coverage can be reasonably priced with some of the higher end models.