how the electrons which are present in outermost shell get coloured by absorb visible light .what happened in excited state

@ jaya 
when the outermost electron absorb some amount of energy in the form of radiation , then it will exicted intoi the high energy level of the same subshell , and in that high energy level , the f centers are there to exhibit the colour of the compound .. 
this is besically called as d-d and f-f transition , 

thakx for your answer but what is meant by f-centers and what reaction had happened there.And how colour is exhibited