A lot of it has to do with the quality of the vendor's kratom. For example, normally I get this local brand from a gas station, it's the cheapest around and their red bali is really good, feels like a mild opiate and lasts a good bit, very little NE effects, relaxing, chill, it's hard to get that crappy dizzy effect from it. The powder is a moderate green color despite being called red bali. I got a brand (twice as expensive) from a head shop the other day, and it says it's red bali, and the powder is brown/red. It fucking sucks in comparison, makes my heart rate go up, feels dizzy, and doesn't do much for withdrawal.
In general reds, red bali or red thai, work the best for opiate withdrawal, as they have the most opioid effects.