the meaning of the colour of output on the linux console depends on what is outputting it. One of the most common coloured outputs is from the program "ls". These colours are defined by the LS_COLORS environment variable which is usually set using the dircolors command. You can see a description of the default colours for ls on your system with the following command
The different colours are used to indicate different file types (often just indicated by their extension) or perhaps their permissions (is the file executable?) or other more subtle characteristics.
Note that users can use different colour schemes with dircolors, typically by making a ~/.dircolors file and invoking dircolors as
eval `dircolors --bourne-shell ~/.dircolors`
in their ~/.bashrc (this example is for bash users).