Where are the actual icons you are going to apply to the folders?
If they are not within a
.dll file, you could make one using the free 30-day trial of IcoFX or some similar software.
Within each folder there is a hidden file called
desktop.ini. They have the file system attributes of S (System), A (Files ready for archiving) as well as H (Hidden). You can see these by adding the Attributes column in an Explorer window.
desktop.ini files look like this for a standard yellow folder:
desktop.ini file in one your [already] customised folder, the important lines are
IconFile, which points to the location of your
icon.dll file that you made, and the
IconIndex line, which points to the particular coloured icon within the file.
You copy the same file to each of the folders you want to customise, but the
IconIndex value will be different, depending on the colour. Make sure that they have the HSA attributes.