I found three Phaser 7800 PPD's after running the Xerox Print Driver v2.82 installer.
Looking at the Phaser 7800DN PPD there is this entry;
*cupsCommands: "ReportLevels ReportStatus com.xerox.ColorCorrections"
So what you could try is commenting this entry in the PPD and then manually adding this modified PPD.
To locate the PPD, open Finder and select Go > Go to Folder. Then type
And then press Go. This will take you to the folder that contains all the PPDs. Browse until you can find the correct Phaser 7800 PPD. Then select it and copy this to your Desktop. This file now on your Desktop will be in the GZIP format, so double-click the file to unpack it. With the file unpacked you can Control-click (or right-click if enabled) and select Open With. If you see TextEdit as an option select it. If TextEdit is not showing, select Other and then browse through the list of applications to TextEdit.
With the file open you can then browse through the text until you see the entry *cupsCommands as shown above. To comment the file out, place the percentage % symbol in front of the line so that it looks like this;
%*cupsCommands: "ReportLevels ReportStatus com.xerox.ColorCorrections"
Now save the file and exit from TextEdit.
The next step is to remove the current printer queue to the 7800 from Print & Scan and create a new queue using the modified PPD. Rather than using the Xerox installer to add the printer you will need to manually add using Print & Scan pane. If you need details how to do this then please reply.
When you get to the step of selecting the PPD, change the Print Using menu to Other and then browse to the Desktop to select the modified PPD. Click OK and then Add to complete the queue creation. Now check that you can print and that you don't get a warning about toner/ink.