For example, in your screenshot, specifically the three under the briefcase, the top 2 haven’t been matched next to yet while the 3 (bottom) has been fully matched next to. All 4 edges will turn purple and the “emblem” will glow.

Have to match next to them until all yellow spots become purple (4x each thing-a-ma-bob). Once all have no remaining yellow spots, they all unlock and disappear!