For maintainability I would not use extended properties for styling (creating inline styles). This goes against the OutSystems best practices.
As it makes it harder for future developers to find where the colour is set.
Rather use the class on cell level to conditionally set the background colour.
(Above example assumes you are developing in Reactive web)
as for traditional web you put the class in the extended properties (Just to point out, you add the class name not the styling)
Kind regards,
Eric