I don't think stable means unhappy.
There are many factors in play with stable / unstable. One of the most important is genes. If I pick a dat in a store, I pick the one wich is displaying good yellow and good black. Whatever tank you put it in, such a dat (in my experience) will allways stay relatively stable. For example when stressed (taking out the tank or something) or in a black tank it will also keep it contrast.
All this keeping the dat in a white enviroment / bright light etc stuff is just making the dat color up so it blends in. Such a dat will still turn black when stressed etc.
Then there's water (probably ph or something plays a role) and enviroment besides the color of it.
Driftwood seems to help in stablizing for some dats, giving the impression that when hiding places are present a dat feels safe to display it's constrasting colours.
Also non shy tankmates (for example clownloach who constantly swim around) help relax a datnioid into a relaxed state and brings him out of hiding.
It does need time to get used to a new enviroment, so while the colour can be stable, the behaviour needs time to really develope in the glass hugger it can be.
My personal experience (and preference) is to have a lot of current in a tank, I feel that this also helps to stabilize a datnioid, but again, if a it is black it will not happen often that such a fish turns bright yellow over night.
I do agree that a stable datnioid is a desirable datnioid. Yellow and black gives a much nicer fish to look at than just black and the frustration it never turns into what it can be in terms of looks. I had a st wich I could not get stable, no matter what I did. I sold him off. Now I have a 4" 3 bar it wich is always stable and has a great colour wich I am much happier about and cost me a lot less and was way less troublesome to get.
Btw not posting this here to start a debate on how to stabilize a dat, just my personal opinion. I completly agree with this:
nomad;4828882; said:
...therefore, there is no universal answer to "stability" and all the threads asking for that are just a waste of time.