Copy darkness on Xerox WorkCentre 3220

I have a WorkCentre 3220 that, on the copy function, just won't seem to make a copy that is satisfactorily dark.  I have the darkness setting to dark and it still will not make a satisfactorily dark copy.  Generally I am copying a laser printer original onto plain colored paper for the bulletins at my church.   Really is a frustrating process to try to get it dark enough for people to read.  We have always used Xerox toner cartridges but that does not seem to make a difference.  I've cycled the machine several times as well.

Any pointers?  Or is this just a common problem with this model?

Thanks,

Leroy