W h e n f l a r e s a r e u s e d a s −−−−−→ a d i s t r e s s s i g n a l s −−−→ b t h e y c o n t a i n −−−−−−→ c c h e m i c a l t h a t p r o d u c e i n t e n s e l y −−−−→ d c o l o r s .