Without being too explicit: as you reveal more of the map, you might notice certain rare things in the pathways that also show up on the mini-map. Their colors are meaningful, and they'll always appear near certain walls...
I had found a little green pixel, so I stood behind a nearby green wall to shine green light on it, and I got the word "Shine" over and over, but I wasn't sure if it was supposed to be "picked up" or anything.
