When trying to print your rota, if the colours of your shifts do not display or do not display correctly, you'll need to turn on 'background graphics/colours' in your print settings.
You should get this option when you try to print, but it's often hidden away in the advanced settings.
Once this is selected, click the print button and your rota as normal.
On Google Chrome, it looks like this:
On Firefox, You will need to turn on 'Print backgrounds', as seen below: