Most dragons color up from a dull or neutral color to their adult color and some high color offspring come out of the egg with just as much color as a full grown adult. I'm been lucky enough to a hatch a lot of dragons with a ton of color right out of the egg, but I've also hatch babies that were almost black, but turned out to be full body yellows! So it depends on the genetics and line as not all lines are the same... For example, certain Citrus lines take up to 6 months or more to start showing the bright coloration they are known for, and other citrus lines show almost directly right out of the egg...
Hope this helps,
Anthony