vector COLOR_1 = <1.0,0.0,0.0>;   // Pure red
vector COLOR_2 = <0.0,1.0,0.0>;  //  Pure green

integer USE_COLOR_1;

default {
   state_entry() { 
      USE_COLOR_1 = FALSE;
      llSetTimerEvent( 1.0 );
   }

   timer() {
       if (USE_COLOR_1) 
          llSetColor( COLOR_1, ALL_SIDES );
       else 
          llSetColor( COLOR_2, ALL_SIDES );

        USE_COLOR_1 = !USE_COLOR_1;
       }
   }
}