How manipulate draw events on widgets specialy Roller

How-to
1

I have roller with for example 5 options. On enter show i set actual active for example 2.
I require leave 2. with other design for example colour on scrolling as mark actual setup .
How do this ?

I try

  lv_obj_add_event_cb(ui_Roller1, roller_mark, LV_EVENT_DRAW_MAIN , NULL);
}

void roller_mark(lv_event_t * e)
{
  if(e->current_target) LV_LOG_USER("Evt begin %d",e->target->class_p);

but how choice object to modify for option 2. marked?