Reds are fermented, that's what gives them the color. I don't think maturity has anything to do with it. Olders leafs might be a darker green as is with all plants but according to the farmers and vendors I've talked to the color all comes down to how its dried/processed. If you never noticed a more pungent smell from red kratom, you probably never had actual red kratom. Or a product that was just very lightly fermented.