The clearances and their colors are for your protection, citizen. Everyone knows about them.
Every citizen of Alpha Complex has a security clearance, indicating their seniority within Alpha Complex and how much the Computer trusts them. There are nine levels: Infrared is the lowest, then Red, Orange, Yellow, Green, Blue, Indigo, Violet and Ultraviolet. (Guide to Alpha Complex, page 7.)
For complete newbie players to Paranoia, it can be fun to not let them in on what the colors mean, but they'll figure it out quick and thisquickly. This trick only works once.
There are rumors about other clearances above Ultraviolet. Rumors are treason.
At least one classic adventure introduces a GAMMA clearance above Ultraviolet. Another adventure has the Troubleshooters infiltrate another Alpha Complex, and discover that there the colors are in reverse priority.