There really is no set in stone answer for why some datnoids are stable and other aren't. krichardson's situation is something I and I'm sure many other datnoid keepers have experienced before where some are bright gold body and pitch black bars while others in the same tank are fully black/brown. Some people have setups that they feel have a higher chance to bring out stability but it's not something that can be relied on 100% of the time.
Personally, I think stability is mostly a matter of camouflage and relates to comfort (not necessarily stress.) My current example, the one datnoid I currently keep, a 4" standard 4 bar Indo with a slightly timid personality was mostly black in the LFS tank I purchased him out of. It was a 20g tank with about 4-5 other similar sized IT and PVC tubes with no lights on in a busy, high traffic, louder store and he was the only one out in the open. After a few minutes of "face time" with him watching me watching him I could make out his pattern and decided that I liked the pattern and his more personable personality from the other IT in the tank and bought it.
Fast forward a few days, he's alone in a 180g tank with lightly dimmed lighting, sand, not bulky driftwood, in a quiet room, very infrequent movement throughout the day and a lot of open space in the tank. He was going back and forward from mostly stable to light brown most days.
He began eating pellets almost immediately (always awesome) and began to associate me with food early on and now about 3 weeks later he's about "85%" stable all of the time and very rarely brown/blacks out. He also makes himself known when he's seemingly asking for food going even more stable to catch my attention when he decides to wait in his feeding corner.
I guess what I'm trying to convey is that in my experience a datnoid that is unstable doesn't necessarily equal a stressed or unhealthy datnoid. I think they are incredibly underrated in terms of the amount of curiosity, inquisitiveness and personality they have and I think it's not acknowledged enough how much they may camouflage themselves simply based on mood and adaptability to their physical environment. For example, I've seen some of my smaller IT in the past flaring their stripes as vibrant as can be and ducking into long grass like plants to sneak up on live worms as if they were an actual tiger blending in the grass. I think they sort of biologically have an idea of how they need to look to best suit their optimal survival.
Another thought I have on it would be that larger datnoids (typically +14") seem to be far more stable far more often than smaller dats. It's just a personal theory but I would imagine most datnoids unfortunately never see the size of +14" but those who do are typically going to be in a more stable (no pun) situation, eat well and often have compatible tankmates and at some point don't feel the need to camouflage themselves into darkness because they know they're cared for, food is coming.
I'm not sure if datnoids going "unstable" is technically a legitimate form of camouflage but I imagine it is and I'm no ichthyologist or biologist but I imagine active camouflage is probably more energy and resource consuming than staying in their base pattern "if that is indeed what 'stable' datnoid's base patterns are so to me, a "survival" technique, going unstable is something they just do naturally.
