A few years after the turn of the century a filing cabinet manufacturer began to sell folders with coloured tabs. This was not a new colour to be used as decoration but a simple, effective way to make visible the index to a folder in a crowded drawer. A red tab on a document would be noticed before a plain buff coloured one, and in a very full drawer that would make a very big difference.
In the mid twentieth century, visible indexing of documents became a subject of great interest to office management. Kardex style filing systems, such as racks and boxes, were designed to hold folder edges or cards so that they could be seen from the front of the rack. The colour of an edge or the coding on a card would indicate the status of a document or its category. The user would not need to read the information on the document, the colour would tell them what they needed to know. This subject is documented on this web site with photographs of filing systems, coloured tabs and cards and other associated items. File Management Software is covered in more detail at https://www.watermarktech.co.uk/file-management-software.
What is particularly interesting about this evolution is how, when offices moved to computer screens, no one ever had a meeting to determine the meaning of the colour red, for example, as being urgent, or amber for pending, or green for approval. Instead, the physical system of coloured folders and tabs was so deeply ingrained that software designers of digital filing systems simply inherited the colour grammar of the physical filing system. There is a useful background explanation of the Science Museum’s collection of office objects.
Today, someone can send a red-tagged document to a shared folder on the Internet with the comment ‘action needed’ in a matter of seconds. They are doing something very similar to what the 1950s office worker did with his coloured strip of paper on the Kardex rail. The medium has changed, the basic instinct hasn’t. File management software today is designed within the constraints of colour expectations that the users bring with them to the software.