I always identify cismontanus (Also called Cassiar, also called Canadian Rocky Mountain) by the overall slate-colored appearance but with the defined hood. Most of the ones I see do have some brown, but I have seen some without. In any case, I would probably call your bird a cismontanus just due to the description. Looking on eBird, the subspecies isn't uncommon in the Arkansas area: https://ebird.org/map/slcjun?neg=true&env.minX=178.56114165787858&env.minY=15.18776539271735&env.maxX=13.67832915787858&env.maxY=72.52451403967618&zh=true&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=all&byr=1900&eyr=2020