I did see in OTN APEX forum question how to highlight an item based on a validation. I have made the solution earlier for that and discussed topic in other post.
I just wrap up solution now here.
If you are on APEX 3 load jQuery library on your page template header.
Go to Shared Components > Templates and filter report by Type "Label".
Copy your favorite label template to new name and edit it.
Or you can define styles using jQuery css method e.g.:
Change form items to use your new label template.
Marko reminding me that validations Error message display location must be set to "Inline In Field" or "Inline In Field and In Notification"..