Some overall advice for setting up an office filing system:
Home Office filing systems are the easiest to set up: The simplest filing system in the world is the "money in or money out", there you have it. If you create 2 alphabetical expanded files or set up 2 file cabinet drawers with alphabetical tabs, you can use these each year and put them in storage after the year has ended. Your bank would qualify for both categories of in and out, so you could set up a special file for it if need be.
Of course in business there is some more complicated information that you need at your fingertips, but you should still keep your filing system down to a simple equation that works for everyone involved. The problem of having a lot of numbers coding and color coding is that if everyone who uses the system is on board and can "easily" access the files, that is great, but if only one or two of 30 people using this system can actually understand and access it, well, it's not very efficient. At mega corporations that have 3 to 15 file clerks overseeing and pulling any and all files the more coding the better!
Color coding is a great tool in business filing systems if you can realistically have everyone abide and use it correctly. If you have a small business this could work very well for you. You just have to be diligent with the people who see it as no big deal whether they grab a blue folder or red one, and keep up with the enforcement. Sometimes it is more of a pain than it is worth and it could well be that it is unrealistic for some of the employees to follow that exact system.
The number one question for any organizational tool to be utilized in any business at all is: Will it actually work for us, is it realistic? Just because you've seen a write up on a great filing system on the web, or at a business you visited last year, doesn't mean it will automatically work for the people who work with your files on a day to day basis. So it is a balancing act of putting together an easy access and efficient system. You should ask for ideas from each department or person that has to have access to these files, because if each one is in a different department they will bring up different needs and usually if taken into account at the beginning set up and updated regularly this will help all involved.