This is what Howell wishes he remembered. [Spoilers for Volume 10]
This is what Howell actually remembered: D's eyes, a bright unnatural purple that made girls go weak at the knees - and a few of the guys too. D's smirk, painted on a few shades darker than his eyes. D walking out of the lab one evening, promising Howell that he'd get something to eat with him the next day, if he really insisted, and never coming back.
This is what Howell regretted: that all he can remember of what D actually looked like is the grainy photo they used in the news when his disappearance hit the headlines, the one of D turning away from the camera, so they got a great shot of D's hair flaring around him in a cloud and the faintest touch of his smile. That he looks at the photo in Orcot's file, and all he can think is So that's what you looked like.