Give them a month or two, jack dempseys really begin to pick up color when they're around 3-4 cm. also depends on their diet. In general, I feed all my fry spirula flakes and black worms once they get about 1-2cm and I find that it brings out the color better. I noticed this after running out black worms, and I fed them only spirula flakes and they dimmed, so I bought some more BW and they got their color back. After mine got their coloration back, I stopped feeding them spirula and they started to loose color again. It's best to try to mimic their natural diet to speed up growth and bring out the bright color. I've never had an EBJD but I've raised a handful regular JD's in the past and they are sort of pale and gold at first (some are dark though from a very small size) and they get more black spots and lines in conjunction with the blue, green and teal scales.