If the writer of said object has not exposed the dxf code for color (62) they may have exposed it to activex. Check the activex properties, you may be able to put the color you want to the object. Start by using -
(if (setq ename (car (nentsel)))
(vlax-dump-object (vlax-ename->vla-object ename) t)
)
What do you see?