I've heard a lot of mixed reports about this. My own experience with a DC250 and DC260 is that they are cack at maintaining colour throughout a job. Either get darker or lighter and change in hue, fade at the edges of the sheet or start toner-starving in the middle.
Make sure your drums are in reasonable condition and that's about all you can do. Keep reporting it to the engineers, but you'll find that this sort of behaviour is 'in spec'.
If it's a really really really important job then I tend to run it in sections - some fronts, some backs, repeat until finished.
If front and back are the same colour then let it run however many sheets it can before the colour goes, pull the paper from the machine and open and close the drum tray. This'll give you another few sheets of proper colour, then you got to repeat.
Alternatively if you know what the machine is going to do - ie turn your red into orangey-brown, then overcook the set-up and make it a very vivid red and by the end of the job it'll merely be slightly muddy rather than bounceable.
Tedious, but then again these ain't production machines. That said, I run the bustled fiery and calibrate off the glass so maybe my set-up isn't ideal!
