If you recently replaced the toner for the printer, or were using non Xerox toner the solution is to enter maintenance mode and run the motor that controls the toner.
You can find the manual to do this by searching online and follow the steps:
GP1- Enter Maintenance Mode
GP29- How to check a dispenser motor
dC330- Component Control
When it says to select the code for the toner dispenser motor the Black Motor code is 093.010 for normal speed 093.011 to run the motor at half speed.
Let it run for about 15-30 "clicks" and then run off 20-30 copies and see if the color comes back to the text.
The black print on our C400 has recently faded to grey.
Why would this happen after such a low copy count when the drums are expected to last 60k copies?