Squirrel-/Soldierfish (Holocentrinae and Myripristinae) are normally a red/grey colour and very secretive.
As to how much they hide, varies from fish to fish, what they do have in common however, is that they are most active when the lights are off, but will, with time, come out more while the lights are on.
Squirrel-/Soldierfish are not generally a threat to other aquarium animals, but will sometimes eat very small fish and invertebrates.
Neither Squirrelfish or Soldierfish are particularly aggressive, and whilst most species can be kept in a small group, they will sometimes fight amongst themselves. In this case, space must be taken into consideration as the Squirrelfish will sometimes chase the less aggressive Soldierfish, if space is lacking.
It is easy enough to get both fish types to eat, but if they do not come out during the day it is best to feed them when the lights are off. In the beginning it might be necessary to lure them out with live food.
Squirrelfish have spikes on their head and gills which easily get caught in fishnets, so avoid those. Being scratched by some species of Squirrelfish can result in an ugly wound and be painful, as some are actually poisonous. If one is not careful when capturing and transporting these fish, their eyes can be damaged.