What is physically happening when some marine fish change color?

[chrissreef]

Maybe these are iridophores and leucophores in action or something else? Two examples I'm curious about;


1. Acanthurus maculiceps (spotted face tang) can be light gray/brown or change to dark with very vibrant yellow spots when excited
http://www.dereksreefshop.ca/images/products/TangWhiteFreckled.jpg and http://s276.photobucket.com/user/CrazyEdie50/media/DSC03314.jpg.html


2. Hoplolatilus chlupatyi - Flashing Tilefish appears iridescent when flashing.
https://www.youtube.com/watch?v=QWSVzUc_XNE&list=FLuRjQTSM3GKnDlB2qnJSlvw
and https://www.youtube.com/watch?v=Iy0ZM8kMOZY&list=FLuRjQTSM3GKnDlB2qnJSlvw&index=2

 

[Sounds Fishy]

I had a sea grass filefish,that was able to change his appearance to fit the background,as a spotted face tang would.I briefly read about it being specialized pigment cells(there is a scientific name for it,however I forget that detail...however I suppose they are iridophores and leucophoes ) that change a spectrum of colour instantly ,on demand.It is a wonderful to watch it happening and very effective way to avoid predators.
The tilefish video is awesome ,and it is trying to attract attention,not hiding,obviously,with that showy display. .