We are often asked to explain digital printing, but to do that we need to go back a little more in history to litho printing. You are welcome to Google a bit but in short the print is printed on something that reminds you a bit of an X-ray film. The image on that film is then burned with UV light on to a photo sensitive plate. The plate is then developed almost like a photo in the good old days before digital cameras. Ink will only stick to the parts of the plate that was not exposed to the UV light.
So this plate is now inserted into an ugly big machine where it is rolled against an inked roller and then against a sheet of paper to produce your printed image. If you want to print in a specific colour you just use the right ink and there you go. Ok you are right it just sounds too good to be true because it is too good to be true. That film and plate is expensive and to get that machine set up to print a perfect image you will have to print 50 or more test prints. When you finally have it all up and running those good old Litho machines are like magic and their printing cost is very low. Normally on a quantity of about a 1000 prints the cost of the consumables on a litho machine start to make sense.
So yes if the quantity is high enough we do sometimes outsource some of our work. However we prefer not to, as we lose control of the process and sometimes even end up having to reprint the job because we are just not happy with the results.
If you now want a full colour job the above story gets repeated four times. Once in yellow than in cyan, magenta and finally in black to create a full colour job. In the old days the colours was printed one at a time on a single step machine. Today you get machines that will do all four colours in one process but again if you got the machine up and running you have to print a lot of pages to get it all to make financial sense.
The problem is we seldom need more than a 1000 copies of the same page so litho is not a good idea any more. Lucky for us digital presses came along. They are very close family of your office laser printer but just bigger and faster, let’s just call them industrial laser printers. So now we can print 500 books each containing 100 pages in full colour and keep the cost down to a realistic amount.