Since players seem to be confused about how to tell the status of possible choices on the Ideology Screen, I am providing this example, from an actual game.
Mobility Rights in Liberty has been already selected, i.e. a Culture Point has been spent on it. None of the others have taken/chosen.
The way to tell is non selected ones have a Black Background in the Name Button that gives the name of the Ideology, while the already selected Ideology (Mobility Rights) has a brighter colored background in the Name Button.
The ideologies that you do not have enough choices in to choose them, are the bottom ones that are a lot darker, i.e. Watchful, Conscription, and Dangerous on the Authority (left) side, and Private Ownership and Enterprise on the Liberty (right) side.
You can select (or choose) any of the brightly lit Names that have a black background in the Name Button.