With conditional formatting, you can do this:
(Get ( WindowMode ) = 2) or (Get ( WindowMode ) = 3)
...as your conditional format and set your fill color to the desired highlight color.
The highlight will appear in browse mode, but not when you print or preview the layout.
You can use Conditional Formatting to change the colour of the field to be different in Browse Mode, so when the user is in Preview and Printing it will no highlight.
The way to do this is, in Layout Mode, select the fields you want to highlight and go 'Format > Conditional...'
Now in the Conditional Formatting dialog click on 'Add' and under the 'Condition' options slelect 'Formula is' and in theformula field type:
Get ( WindowMode ) = 0
Now under the 'Format' section specify 'Fill Color:' and choose a colour you want to highlight the field with. Then click 'OK' and job done.
I hope this helps
Ah, excellent! Thank you both for helping me see the light!