This is what I use to set to bylayer:
(if (setq ss (ssget "x" '((0 . "*DIMENSION"))))(command "_.dimoverride" "dimclrd" 256 "dimclre" 256 "" ss ""))
(if (setq ss (ssget "x" '((0 . "LEADER"))))(command "_.dimoverride" "dimclrd" 256 "dimclre" 256 "" ss ""))