Two things about Wizard plaques: you always have to cast right spell on the place with plaques and you always have to exam them (Enter). When there's some kind of cup under plaques, cast Incendio, and the cup will become a lamp so you can take a closer look at the plaques. In other cases look for distinguishing fragments of wall and cast Accio on them.
That kind of highlight means "cast Accio on me".
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