From "Holodeck, Part 2"
Atka dropped her strike rifle and whipped out her pistol, blasting it in the arm. Realizing that without her shotgun, she couldn’t actually sever it easily, she panicked, firing at it again, and doing...something else. There was a spark of blue energy around her head, and her eyes seemed to glow blue for a moment. A thin, almost invisible, thread of energy struck out at the Outsider’s head but then dispersed. This was because, being a construct of light, it was not affected by the power Atka had just manifested.
And afterwards, from "Whispers of Power, Part 1"
Desmond looked at her, and shook his head. “Not everyone would agree.” Desmond closed his eyes and began his usual stance. He slowly built up and released psionic waves so that the purple glow appeared around his body. He held out his hand and the rotating ball appeared once more in his palm, rotating at high speeds. “This is what years of training has accomplished, and this is not even scratching the surface of my research.” He gave her a stubborn look, “How do you think the lab techs, engineers and soldiers would react to this?”
Still purple, Marine.