Tonya

It might represent how they're seen by people around them and the people they are. Albert was always elegant and intimidating. He was in control of his actions and his experiments. He was mysterious, he didn't show his emotions most of the time. Black represents darkness, power, authority. Everything that Albert was.

Meanwhile, Alex is usually seen wearing white. The color represents purity, perfection, and goodness – everything that Alex wanted Spencer to see in her just to betray him later. Spencer trusted Alex more than he trusted Albert, showing her all the experiments that her brother didn't get to see and she used that to her advantage. The small parts of black and red in her outfits would represent the hidden darkness under the innocence.