Not sure how you keep the humidity up.. but lowering the humidity is not the best of ideas - however NOT having mulch that is "saturated" wet IS a good idea. I also use cypress mulch and keep mine humid by spraying their carapace directly [ till they drip ] 3 to 99 times a day.. whichever comes first! "Drier" mulch is better than "wetter" mulch.. so the fungus does not develop.
Cherryhead redfoots 'usually' start showing the marbling right at one year old and it 'usually' peaks at 18 - 24 months old.. then it 'usually' fades from there. I say 'usually' because there are always exceptions and extremes.


Neither of these were "started" by me so they tend to be a little bumpy. They were both a few months past 2 years in the pics.. but now at 3 years old [ and outside for the past 3 months ] their "marbling" is much deeper and shows little unless wet and then very little in comparison. Again there are always exceptions and extremes.
Terry
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Terry
Turtletary.com