Hi! Here is some info from the Quark knowledge base
Applies to: QuarkXPress 7.x Mac OS, Windows
Problem Description: When I open a QuarkXPress 6.x project in QuarkXPress 7.x, the Yellow color displays with a lime green tint.
Background: This display issue occurs because the QuarkXPress Color Manager is always ON in version 7. When you open a legacy document, the problem occurs when the Color Manager is set to QuarkXPress 7.0 Default. You can change the Color Manager preferences to emulate legacy QuarkXPress treatment of color information if you make changes in your display and Color Manager settings.
Solution: To set QuarkXPress 7 to treat color in the same manner as version 6, change the Monitor Profile from Automatic to QuarkXPress Legacy RGB (QuarkXPress/(QXP Windows:Edit) > Preferences > Display > Monitor Settings). If this fails:
Open the version 6 project in QuarkXPress 7.x.
Go to QuarkXPress/ (QXP Windows:Edit) > Preferences and select the Color Manager pane.
In the Source Options area, choose QuarkXPress 7.0 Default from the Source Setup drop-down menu
Good luck!