if the jd was in a tank with other jds his dark color prolly was cause he was the dominate or one of the dominate's now he is takin out of that tank he lost his color cause he isnt the dominate one anymore mine did it when i first got him an he was the same size.
My JD did the same thing. He was darker when I brought him home, then last week he appeared lighter, now today he was darker. Its crazy how they can change colors with mood or surroundings.
Mine changed color alot when it was younger.
Now at almost 3 years old, rarely changes color, just stays dark most of the time.
As stated previously there are many reasons for color change.
I think your light substrate has some to do w/ it staying light in color though.
americans are different from americans .. africans wont loose ther colour if there in light substrate americans sort of blend in with there surroundings