They look like "identification layers" to me but some may also define doping (or prevent, like "high resistivity poly" which could be nothing besides in-situ doping.
It is easier for CAD rules development if you build easy recognition (and parameter reflections, though this is not as popular in CMOS it seems) into the PCells.
DRM - Design Rules Manual you can find in PDK documentation
To open tech file, you can use Technology File Manager, which should be accessible from CIW->tools menu