Can just BARELY see ghosts in total darkness.

code/modules/mob/dead/observer/observer.dm

@@ -1,3 +1,7 @@
+#define GHOST_DARK_ALPHA 10
+#define GHOST_LIGHT_ALPHA 255
+#define GHOST_DARK_CUTOFF 1
+
 /mob/dead/observer
 	name = "ghost"
 	desc = "It's a g-g-g-g-ghooooost!" //jinkies!
@@ -95,6 +99,22 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 		ghost.timeofdeath = world.time // Because the living mob won't have a time of death and we want the respawn timer to work properly.
 	return
 
+// In darkness over a certain threshold, ghosts become slightly visible for the spooky value.
+/mob/dead/observer/proc/amInDarkPlace()
+	var/turf/simulated/T = get_turf(src)
+	if(!istype(T))
+		return 0
+	if(T.lighting_lumcount <= GHOST_DARK_CUTOFF)
+		return 1
+	return 0
+
+/mob/dead/observer/proc/updateSpookyAlpha()
+	if(amInDarkPlace())
+		alpha=GHOST_DARK_ALPHA
+		invisibility=0
+	else
+		alpha=GHOST_LIGHT_ALPHA
+		invisibility=INVISIBILITY_OBSERVER
 
 /mob/dead/observer/Move(NewLoc, direct)
 	dir = direct
@@ -102,7 +122,7 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 		loc = NewLoc
 		for(var/obj/effect/step_trigger/S in NewLoc)
 			S.HasEntered(src)
-
+		updateSpookyAlpha()
 		return
 	loc = get_turf(src) //Get out of closets and such as a ghost
 	if((direct & NORTH) && y < world.maxy)
@@ -116,7 +136,7 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 
 	for(var/obj/effect/step_trigger/S in locate(x, y, z))	//<-- this is dumb
 		S.HasEntered(src)
-
+	updateSpookyAlpha()
 /mob/dead/observer/examine()
 	if(usr)
 		usr << desc