I can't say why it happens, but I can offer up my observations and what I'm doing. I've been wanting chime in here all weekend but am just sitting down with the laptop this was going to be too long to type out on the phone.
1989-1992 we got a pair after a long wait. Correction - my dad got a pair of WTC (supposedly from the Marshalls). We put them into a ritteri, had absolutely no issues with acclimation, no Q, etc.. and we kept them until the tank was shutdown and they were resold (in San Diego FYI). They held the black body/orange finnage and white tails the entire time. Let's say back then Dad wasn't as fancy as I am now. We kept the tank at 1.023, used IO, 82deg, and 60 watts of NO T12's. Great for the fish, ritteri's not so much - typical 6 month slow decline. Fish fed only prime reef/F2 and brine shrimp (not fortified). The pair spawned from 1991-1992 and memory is a little hazy but they were in the 5" and 4.5" range? There were other fish spawning as well which I think is a good indicator that the system was doing well.
Fast forward to 2010.
Always wanted to give WTC another shot so decided to commit to the search. Knowing their current reputation for being difficult (and a whole lot wiser overall btw) I got a few of them (solomons) and put them into my Q system. Unfortunately they dropped like flies losing 5 of 6 within 30hrs. It was bad. The lone one to make it was very very hurting and despite repeated dipping, formalin baths, hypo, the works I finally gave up at about 48hrs into it and coiled up the hoses and gave up. Well that fish lay on the bottom for another 2 days before starting to stand back up. OK something to work with! After 6 wks in the Q including hypo, 2 courses of prazi, and M2 (freshwater) for some other issues, that fat sassy WTC went into the DT with absolutely beautiful colors. Black body color, orange finnage, white tail. In Q there was no direct light, 80deg, and food consisted of NLS pellets, enriched brine, hikari/PE mysis. I slowly transitioned out of hypo to 1.025 and when the DT and Q matched I moved it over. It took about one week for the fish to set up shop in the magnifica. It wanted in, but was getting stung to high heaven I believe based on what I was watching.
Within 2 weeks of being in the DT the color started to change. I took a work trip and 2 weeks later when I came back the fish was brown, finnage dull orange, and a dirty white tail. Only thing that got better were the blue stripes. Fish showing HLLE? signs as well with forehead pitting and lateral line more visible in the 2nd stripe. My DT is a primarily SPS setup, 1.025, 2x250W MH 20K, nem/fish combo in ~400 umol, IO with typical reef chemistry numbers, very clean system with minimal fish load. Stepped up feeding to NLS pellets, NLS thera-a, enriched brine, hikari/PE mysis, F1, F2, prime reef flakes, cyclops, in an attempt to counteract the HLLE. I do believe during December and here in January it's slowly gotten a little better and the washed out brown is more like a deeper chocolate brown. Finnage still drab. Interesting to see which way it goes moving forward.
What I can't say is whether or not the environment had anything to do with the color. Looked fine for the 6wks in the Q, but would it have changed shortly thereafter had I left it - I'll never know. Is it the nem? well one time they stayed black, the other not. Salinity - 1.023 with a swing arm may have been today's 1.025 with calibrated refractometer? Food even has some overlap. Lighting is definitely different, temperature is close. Corals now, that's another difference - no carbon used in either system - so could be chemical. Or something altogether different. I mentioned the hell the fish went through in Q - big difference as well.
So to summarize, my first experience resulted in WTC's that looked very close to the ones in Wilkerson p.144. This second experience resembles Jordan's spawning video.
Now for the YTC pair in the Q now
