Updated: Dec 23, 2020
Just a quick little post before the holidays. Most of us are familiar with Field Styles, and Field Styles have been around in the Platform UI (forever) and the Workspace UI up until the Orlando release. Field styles allow for all kinds of great CSS and can be hooked into Script Includes for complex logic of when to show them. Highlights do look a ton better than Field Styles and the fact that they are workspace specific is amazing, preventing the need for any kind of weird view trickery with Field Styles. The downside is that while Field Styles applied to both Platform and Workspace UI previously, you will be configuring for each UI now. I did some poking around on my PDI, and it looks like Field Styles no longer apply to the Workspace UI. So that's new and good to know before spending countless hours wondering why the red dot you configured isn't showing up!
Highlights only apply to lists at the moment, but that's ok because Field Styles in Workspace UI didn't allow for styling of the form view either, so we're not really missing anything there in the transition.
Here's a quick one I configured to turn Short Description on the Case form green or in Highlights terms Positive, based on Priority is 1 - Critical for demo purposes:
The Value Override feature is pretty neat as it allows users to replace field value text, this would be for display purposes only, and wouldn't change any values in the database. As you can see in the screenshot I was able to override my Short Description values. I'm unsure if you can script here to get the current value and append to it, I'm going to say no and say this probably still has to be done with scripts, but maybe.
Interestingly enough, I don't think you can create your own Highlight values, right now ServiceNow provides 7 to choose from. I poked around in the Highlighted Value Condition (sys_highlighted_value_condition) table and didn't see where any CSS or colors are linked up. If someone knows please shoot me a comment. Also note per the docs, you cannot highlight Reference, URLs, and Document IDs. Despite these limitations, it seems like Highlights can be meet most Workspace needs.
So head on over to the Highlighted Values module under Workspace Experience > Administration and go to town with creating the styles you want specifically for your workspace.
ServiceNow Documentation: Highlight List Fields