The default printer driver set to a black and white printer. Excel uses the default printer settings to create a high quality picture of the schedule.
Try the following:
• Close all Office programs
• Open Control Panel | Devices and Printers
• Change the default printer driver by right-clicking on a different printer and choosing Set as default printer
• Reopen Office and try sending the schedule again
If the users are not connected to a colour printer you can set Microsoft Print to PDF as their default printer.