Why is chloroform kept in dark coloured bottles?

Chloroform is slowly oxidised by air in the presence of light to an extremely poisonous gas phosgene. Thus it is stored in closed dark coloured bottles completely filled so that air is kept out. 2CHCl3(Chloroform) + O2 + Sunlight → 2HCl + 2COCl2(Phosgene)