What is far more bizarre is that one of Padra's brothers has "dark hair from his wetlander side".

His only "wetlander side" is Rand via Tigraine (so to speak as Rand is half-Aiel by blood, not a pure wetlander). Tigraine is a blonde (her brother is a redhead). More importantly Rand is a redhead, so he has to carry a pair of recessive genes.

I don't think it's even possible short of a genetic anomaly for a blonde like Aviendha and a redhead like Rand to produce a child with dark hair and colouring as Brown is dominant over both. If Tigraine was carrier of one brown gene, she'd have had brown hair. It sounds like Brandon wasn't careful with the genetics in that chapter, or worse he messed up and was thinking of Tam as the "wetlander side", forgetting as he wrote that Tam isn't Rand's father and Rand's father, not mother was Aiel (and that in the TR where blondes and red hair are totally unknown it's most unlikely Tam would carry a recessive gene for blonde hair anyway...)